Getting solid control of idle speed is essential if you want to provide aftermarket tunes with OE idle quality. In this webinar we’ll discuss the various options for controlling idle speed and look at how we can configure them in the ECU. We’ll also look at the best approach to tuning the idle control system to get stable results regardless of the operating conditions.

For this webinar we will be using our Nissan 350Z with the Link G4+ ECU

00:00 - Welcome to this webinar, I'm Andre from the High Performance Academy and in this webinar we're going to be looking at the idle speed control functionality on the Link G4+ platform.
00:12 And for today's webinar we're going to be using our Nissan 350z which does control idle speed by using a driver by wire or e throttle throttle body so we're going to be looking at how that applies on the Nissan VQ35 engine.
00:27 We'll also be discussing the other common techniques for controlling idle speed and we'll have a practical look at how we can can go about adjusting and optimising our idle speed control.
00:40 Now before we get started, let's talk about what idle speed control is and why we need it in the first place.
00:48 And I mean that might sound like a fairly basic question but a lot of tuners don't really fully understand or appreciate why we actually need some way of adjusting and controlling our idle speed in the first place.
01:02 And certainly there are a range of race only applications where the added complexity of an idle speed control system is deemed unnecessary and these engines can run adequately without any idle speed control functionality whatsoever.
01:19 Now first of all, what we're trying to do here, in my opinion anyway, this is my own personal approach to tuning is always to replicate OE drivability.
01:32 Now that's the sort of drivability where we can reach in the window, the driver's window on a freezing cold morning, turn the key when the engine is still stone cold and have it start perfectly and assume a normal idle speed.
01:47 We also want that situation where when we pull up to a set of lights and put our foot on the clutch, the idle speed doesn't drop and almost cause the engine to stall.
01:57 Likewise when the air conditioning switches in or perhaps the engine fans, or we turn the steering wheel and use some of the load, it adds some load using the power steer pump, we want our idle speed to be relatively consistent and stable.
02:14 All of the things we would expect with a factory fresh car, straight off the showroom floor.
02:21 Now obviously in some heavily modified engines, this may not be achievable but in my own experience with the engines that I've worked on, by far the largest majority, if we want to take the time and do our job correctly and utilise the functionality available in the ECU, it is perfectly possible to replicate OE functionality with our idle speed control system.
02:48 Now to the end user of that car it's really going to make the difference between a car that's easy to drive and nice and enjoyable to drive and one that's a real burden where we're always worried about the thing stalling when we pull up to a set of lights.
03:02 And that's really frustrating, so that's what I'm trying to achieve.
03:06 Let's look at why we actually need idle speed control because understandably if the engine's idling and it's at a normal operating temperature, there shouldn't really be any need for us to vary the amount of air entering the engine to affect the engine's RPM, it should be relatively stable.
03:28 And while that's probably a fairly good point, there are a range of situations where we may need to increase the amount of air bypassing the throttle plate in order to control that idle speed.
03:41 The first of those is when the engine is cold.
03:44 Now first of all, when the engine's cold, we're going to probably need to bypass a little bit more air just to maintain the same engine RPM that we would use when the engine's hot so let's say at 80 or 90°C engine operating temperature, we might want to idle at 800 RPM.
04:05 If we also choose to idle at 800 RPM when the engine's operating at 10° engine coolant temperature, we're going to almost certainly need to bypass some more air at that cooler temperature in order to achieve our 800 RPM target.
04:22 More likely though is that when the engine is operating at a cooler temperature like this, 10°C for example, we're probably going to actually target a higher idle speed.
04:34 Now the reason we're going to target a higher idle speed is because the engine isn't going to operate as smoothly and as nicely when it's cold, we don't get quite as good atomisation of the fuel when the intake ports and the cylinder head are cold so the fuel is dropping out of atomisation.
04:54 So generally a higher idle speed's going to improve our air velocity and that's also going to help the engine run better when the engine coolant temperature is low.
05:07 So those are the two reasons why we're going to need some form of idle speed control there just based on our engine coolant temperature.
05:15 That's not the only thing that requires idle speed control though.
05:20 Even when we're sitting at a stable engine coolant temperature at our normal operating range, we also have a range of functions that will apply differing loads to the engine.
05:31 So let's say for example a great one there might be our air conditioning.
05:37 So if our air conditioning compressor clicks in and out, locks in and turns on, this is going to apply a mechanical load to the engine which tends to drop our idle speed and we want our idle speed control functionality to be able to account for that and increase our air bypass to maintain that idle speed when our air conditioning comes in and out of operation.
06:03 Likewise our engine fans, while that's generally a lower load, it's an electrical load, so that's accounted for by the alternator charging, we're still likely to see our engine speed drop when our engine fans switch in and switch out and the alternator draws more power from the crankshaft in order to maintain its charging voltage.
06:29 Next we've also got to consider aspects such as our power steering.
06:34 When we turn the wheel and we draw power from the engine in order to operate our mechanical power steering, this again is going to drop our idle speed and the last function that I'm going to talk about is in an automatic transmission we're going to tend to see the idle speed fluctuate as we move from part or neutral and pull the gearbox into gear.
06:58 This applies some load through the torque converter and hence we're again likely to see our idle speed drop.
07:05 So these are the functions or requirements that are why we include idle speed control in the first place.
07:12 So all of this idle speed control tuning is about maintaining a stable idle speed control as these particular functions switch in and out and the load on the engine at idle varies.
07:29 OK so let's talk about the options we have for idle speed control.
07:34 And really what we're trying to do here is control the amount of air entering the engine.
07:40 So typically we're going to have a throttle plate blocking the air and at idle we're obviously going to have that throttle plate close or very close to being closed.
07:50 So the 3 main techniques are for adjusting the airflow into the engine.
07:56 In more recent years, and this is the one we're going to be looking at in today's webinar, we've used the drive by wire or electronic throttle body to physically move the throttle plate and adjust the airflow into the engine.
08:09 It's very effective and it also doesn't require a separate idle speed control circuit in order to function so we're seeing that in more and more late model cars.
08:20 In the early days of drive by wire throttle, the early drive by wire throttle bodies still tended to incorporate a second idle speed control circuit but now we only see the throttle body itself.
08:35 So on older cars though without drive by wire or if we're building a project car and we're using a cable throttle body, the common techniques would be to use an air bypass solenoid or idle speed control solenoid that will bypass air around the throttle plate.
08:52 So essentially it's taking air from the inlet side of the throttle body.
08:57 Here we want to be really taking filtered air as well, that's important.
09:02 And then we're going to bypass that to the plenum side of our throttle body.
09:08 And likewise the other common technique is a stepper motor.
09:13 These are particularly used, a common one there that springs to mind because I'm familiar with them is the stepper motor idle speed controller's very popular with Mitsubishi, they've been used for a number of years.
09:27 OK so those are our 3 techniques and really what we're going to use will be dependent on the engine that we're tuning.
09:35 I will point out that we are going to have questions and answers at the end of this webinar as usual so if anything crops up that you'd like me to explain or you want me to elaborate on anything that I've talked about during the course of the webinar, please ask those in the chat box and I'll deal with those at the end of the webinar.
09:55 Now another aspect that has become common with our idle speed control is to also incorporate as well as the actual air bypass, also incorporate idle ignition control.
10:09 And what we're doing here is using the ignition timing at idle to influence the amount of engine torque being produced and this can be very powerful to give us an instantaneous response to any error in our idle speed control.
10:26 Now I'm just going to go through that very briefly because it is a very powerful way, when we include this in conjunction with well tuned idle speed control circuit, it's a very powerful way of achieving rock solid idle speed control.
10:43 Now what I'll do is I'll just start our engine here and we'll go to our PC Link tuning software and I'll just jump online here.
10:53 Now I'm not going to give a thorough description of the idle ignition control during this webinar, we actually have already run a previous webinar that focused solely on idle ignition control on the G4+ platform so if you're interested in learning more about this function and how to utilise it, please search for that in our webinar archive, it's definitely worth viewing.
11:20 But what I'll do is we'll just go to our idle ignition control setup here.
11:25 And what we can see is first of all we've got our idle speed, idle ignition control turned on and we've got a range of lock out parameters so this is where the idle ignition control will actually be active.
11:39 Now I'll just go to our idle ignition table.
11:43 So what we can see here is we have a 2D table and what we've got is our idle target error as our X axis so that's our values here.
11:55 Essentially all this is, is the error between our target idle speed and our current engine speed.
12:02 And what we can see is at this point here at 0, this is when we've got no error, so this essentially means that we're right on our idle speed target.
12:10 As we move to the left here, this means that our idle speed is above our idle speed target.
12:19 So our engine speed's a little bit high and likewise to the right hand side, we can see that our idle error is positive.
12:29 This means that our idle speed is a little bit lower than our target.
12:33 So the point of this is what we're relying on is the fact that as we increase our ignition timing, we're going to, increase our ignition timing towards MBT, we're going to increase the torque that the engine's making.
12:49 This is absolutely no different than tuning our ignition timing anywhere else in the map.
12:56 So as we increase our ignition timing towards MBT, we're increasing our engine torque and naturally this will result in the engine RPM increasing.
13:04 Likewise, as we decrease our ignition timing, as we retard our ignition timing and move further away from MBT timing, we're going to reduce our engine torque and this will tend to drop our idle speed.
13:18 So what we're doing here is constantly varying our ignition timing to adjust our engine torque and hence our idle speed while we've got an error present.
13:28 One thing I will touch on before we move on is if you do want to use idle ignition control, and I do urge you to make use of it, we need to make sure that our base ignition timing, when we have zero idle RPM error, so when we're at our target, we need to make sure that our ignition timing is retarded from MBT.
13:52 Now the reason for this is if we're sitting at MBT timing, it gives us no potential to advance the timing and increase our engine torque.
14:01 So for example here you can see that at zero error I've got a value of 12°.
14:08 So it's fair to say that that's going to be well below MBT and in this particular engine we find that MBT is somewhere around about 24 to 28° at our idle speed target.
14:21 So we need to be retarded from that MBT value so that we can move the ignition timing both advanced and retard in order to achieve a stable idle speed.
14:32 OK so let's move on now and what we're going to do is talk about a procedure for tuning our idle speed control.
14:44 As I've said, in our 350z we're going to be doing this using the drive by wire throttle control.
14:49 And what we want to do, any time we're tuning our idle speed control system, I always want to start with the idle speed control system tuning in open loop and this means that the ECU isn't going to be making any adjustments to our idle speed control circuit so we're not going to be masking any errors by the ECU's closed loop control system.
15:17 Now when we're looking at this, this is really no different to tuning any feedback control system in the ECU, let's say boost control for example.
15:26 What we want to do is set the open loop idle speed control so that it's as close to our target as possible and it's doing as good a job as possible and if we do our job correctly here in open loop, when we reenable closed loop control, this is going to mean that the ECU has very little work to do and the less work the ECU has to do in closed loop, the more stable and accurate our idle speed control system is going to be.
15:55 So let's go through our setup first of all, and I've got our ECU settings menu popped out here on the left hand side.
16:04 Couple of ways I like to use this, I generally tend to just type in the table that I'm looking for, it's really quick and easy.
16:12 However in the menu structure we can click here on our idle speed control and this is going to open up all of the functionality under our idle speed control sub system.
16:24 And let's start by looking at our idle speed control.
16:28 So this is all of the base settings here.
16:31 Now for a start, we've got our idle speed control mode and this is going to be dependent on the type of system we're tuning.
16:38 Essentially we have open and closed loop here for e throttle and we also have open and closed loop here for our solenoid or stepper.
16:47 And the settings you're going to use there, understandably are going to be dependent on what sort of system you're tuning.
16:53 Now what I'm going to do here is just set us to open loop control mode.
16:59 Now we're going to get our engine speed, idle speed under control very shortly but let's just go through the rest of the options in our menu here.
17:09 Next we have our base or target table mode and we can select here a 2D table.
17:15 So this sets our base idle speed position and this allows us to use, typically we're going to, I've always used a 2D table here which just sets up our base position relative to engine coolant temperature.
17:31 If we set up a 3D table, we can also adjust our base position relative to our idle speed target as well.
17:40 If you really want to get very precise control.
17:42 I'm just going to leave that at our 2D table at the moment.
17:49 Next we have our accelerator positon or throttle position lock out.
17:53 And again this depends on how our idle speed control system is going to function.
17:59 So if we're using a drive by wire throttle body as we're doing here, this is going to be based off our accelerator or the driver's throttle pedal position.
18:09 And what we're trying to do here as well as with our next setting is we're going to try and make sure that, actually just going to jump back to closed loop so we can also include our driven speed control.
18:26 What we're trying to do with this setting here is make sure that our idle speed control system is only actually functioning when we want it to be.
18:36 So we really only want the closed loop control system to work when we're actually at idle.
18:42 So this particular setting, our accelerator pedal means that as the driver's foot pedal position is above 2% then the closed loop system isn't going to function and what this means is it's going to prevent the closed loop control system from trying to correct what the driver's actually doing on the foot pedal.
19:00 So we're going to assume if we're below, in this case 2% throttle then we're completely off the throttle and we actually want the engine to enter idle speed control.
19:10 Next we're going to move up to our speed lock out here.
19:15 So this allows us to also disable idle speed closed loop control when the engine, when we're actually rolling.
19:24 So in this case, what I've done is I've disabled our idle speed closed loop control any time we're above 10 km/h.
19:32 So this prevents the idle speed control from trying to reduce our idle speed if we're, for example, just rolling down a hill, rolling along a straight piece of road, in gear at perhaps 40 or 50 km/h but we've got our foot completely off the throttle.
19:50 So if we didn't disable our closed loop control here then the closed loop sub system is going to try really hard to bring our idle speed or our engine RPM back down.
20:00 And what this is going to result in, the most common situation we see here is we're rolling up to a set of traffic lights and we're off the throttle, we're only just barely cruising along and as we come up to the set of lights, we put our foot on the clutch and what's happened while we're been rolling along is the idle speed control closed loop system has been trying to close down the throttle or close down our idle speed solenoid or stepper in order to reduce our engine RPM and then when we put our foot on the clutch, because our idle speed control circuit is essentially completely closed, we find that our engine stalls immediately, it's a really common situation and using our speed lock out is a great way of fixing that.
20:46 Next we've also got an RPM lock out and again, this is just another process that helps to make sure that the idle speed closed loop control is only working where we need it.
20:58 So this RPM lock out works above our idle speed target.
21:04 So let's say for example we had an idle speed target of 1000 RPM and in this case we've got an RPM lock out of 500 RPM, if we end up with our engine speed above 1500 RPM the closed loop control system won't function.
21:20 I've generally found in this case, a lock out of 400 to 500 RPM above our target generally works quite well.
21:28 Next, moving down we've also got some steps for our engine fan and our power steering.
21:35 So these are increases that will be made to the base values in our idle speed table when our engine fans step in or our power steering is functioning and we can tune these values here in order to maintain a stable idle speed as these functions step in and step out.
21:58 We can see also one that I haven't used here is our neutral park step and this is used when an automatic transmission steps in or out of gear as I've already discussed.
22:15 OK so this is our base setup and as I've said, we want to start by making sure that our system is in open loop so we're not going to mask any errors in our base table with the ECU's closed loop control system.
22:35 So that's a really important first starting point.
22:38 I'm going to go through the process as if we're tuning the car for the first time and the process here would be that we're going to obviously tune the fuel and ignition tables for our engine on the dyno so we're going to have our engine at a normal operating temperature.
22:53 So this is the first place we're going to start is achieving a normal idle speed at our normal operating engine temperature.
23:03 So what we want to do is start by going to our idle target RPM table.
23:11 So this our first place that we want to go after we've set up our base parameters for our idle speed control.
23:17 Now this idle target RPM table is only used In closed loop but we want to reference this while we're tuning in open loop anyway.
23:28 And it's really important to set this table with realistic values so this is one of the most common mistakes I see tuners make, they're trying to make the engine idle at unrealistic RPM.
23:40 So for example with a 4 cylinder engine with a small displacement, perhaps with a relatively aggressive cam, it's probably reasonable to expect that that sort of engine combination might want to idle somewhere between maybe 1100 and 1300 RPM.
23:58 If I use my old drag car as an example, that was a 2 litre Mitsubishi 4G63, cams with around about 300° advertised duration.
24:09 That engine idled at 1800 RPM.
24:12 So with these sorts of engines, if we tried to achieve an idle target of perhaps 750 RPM, we're just simply not going to be able to get the engine to idle happily there.
24:23 And we're going to waste a lot of time so the first point is to make sure that our idle targets that we're choosing are actually realistic and achievable by the engine.
24:35 So in this case we can see that we've got a 2D table we can change our target RPM relative to engine coolant temperature.
24:44 You can see in the main areas where the engine is up to normal operating temperature, with our stock VQ35, I'm targeting 800 RPM and that's relatively close to the stock idle target.
24:58 At lower engine coolant temperatures though you can see that I'm targeting that higher engine RPM as I've already explained, this tends to make the engine run smoother when it's cold while it's coming up to temperature.
25:13 And then all I've done is I've used a linear interpolation between our low engine coolant temperature and our normal operating coolant temperature to drop that idle speed away as the engine heats up.
25:25 So again, right now in open loop, this table wouldn't be used but we are going to use this as a guide to our tuning.
25:35 OK so the next table we're going to look at is our base position table.
25:40 What we'll do is click on our idle speed control here and what we're going to do is go through to our idle base position table.
25:49 Now for a solenoid or stepper, this will be our solenoid duty cycle or our number of steps with a stepper motor so we're going to see numbers potentially much higher than what I have here.
26:02 Possibly numbers in the range of 30 to 100 with a stepper motor we may see numbers above 100 so the numbers are going to depend on your type of system.
26:15 And if we look at a solenoid for a good example there, the duty cycle there can vary between 0% and 100%, 0% typically would have the solenoid completely closed and 100% would have the solenoid completely open.
26:31 And the idle speed will vary based on how much air that solenoid is able to bypass when it's completely open.
26:39 Here we're talking about e throttle or drive by wire throttle opening so of course we're looking at much smaller numbers and if we started our tuning for a drive by wire idle speed control system with simple numbers that we might expect to see in a stepper or solenoid system, we're going to end up with our engine sitting on the rev limiter very quickly so it's important to understand that distinction and make sure that our numbers are suitable and we'd really want to do that even before we started the engine for the first time and got it running.
27:13 OK so we can see that we're sitting at our operating temperature now.
27:18 And we've got a couple of ways of adjusting our idle speed.
27:22 What we can see right now is our idle speed is actually sitting a little bit above our target, we're sitting at about 860, 870 RPM and remember that our idle speed target was 800 so what we can do in order to adjust this is simply reduce the idle speed values, sorry the base position values in our target table here and you can see that as I do this, it has dropped our idle speed now and we're sitting at about 830, 820 RPM.
27:58 There is a really important distinction with the way we tune our idle speed control targets that's only used with a drive by wire or e throttle control system.
28:12 What we want to do there is actually use our e throttle target table at operating temperature to achieve our target idle speed when we've got basically this table set to zero.
28:27 So what I'll do is I'll just swap over to our e throttle target table and we can see that here.
28:34 And we can see that our top row of this table at 0 accelerator position, you can see that the values in this table aren't set to zero.
28:45 You can see particularly here, at idle we've got values of around about 4% so we want to adjust these base values here until we're right on our target so I'll just drop that back down to 3.5% and that's got us down to our target.
29:02 So remember we want to make these first changes and get our idle speed control working with the system in open loop.
29:12 We don't want our closed loop control system to be affecting our results.
29:17 So what we want to do is adjust our base position table until we're really close to our idle speed target now I know I've cheated here because I reenabled closed loop control just to show you a few other functions in that idle speed control menu but when we're actually tuning this from scratch we want to start with our closed loop control disabled so we want to set our idle speed control base table in open loop.
29:47 So we've done this now at idle with our engine at normal operating temperature.
29:53 Once we've done this, we can then go through the same process as we warm the engine up.
30:03 So there's two ways I like to do this, we can either do it with open loop, in our open loop mode.
30:10 So again we've got no feedback from our closed loop control system and what we can do there is simply allow the engine to go cold, normally we need to do this overnight and then start the car and what we want to do is straight away go to our idle base, oops not that one, we want to go to our idle base position table and we want to be prepared to make changes to this very quickly.
30:37 So again, we're starting in open loop mode and we may be down somewhere around about 0-20°C and what we want to do is start the engine and immediately watch the idle speed once the engine starts up and adjust our steps until our idle speed matches our target.
30:59 And essentially I'm going to spend my time while the engine comes up to normal operating temperature, sitting in this table and adjusting the individual cells as we move through.
31:12 So if we start at 10° we'd adjust this particular cell until our idle speed matches our target and then we'd allow the engine to warm up to 20° and again we'd adjust our 20° cell so that our idle speed matches our target and we can just simply do this through until we come up to our normal operating temperature.
31:33 And this is going to do a really good job of filling this table in with the actual values our idle speed control circuit needs in open loop.
31:42 Remember at this point again we're in open loop.
31:46 Couple of tricks when we're filling this table in, obviously if I can only get down to 10 or maybe 20°C this is a real big problem in areas where we have large swings between summer temperatures and winter temperatures.
32:00 Here in Queenstown's a great example, in the summer, even on a cold morning we may only be able to get down to 15 or maybe 20° engine coolant temperature so this means that we may only be able to start our tuning process here in the 20° cell.
32:17 In the middle of winter however, it's not uncommon to see our engine coolant temperature down around 0 or even below.
32:25 So if we're tuning an engine in the middle of summer, what are our options here? Well we may not be able to get it completely perfect but what we're going to tend to see with these particular tables is a bit of a trend and if I just look at this graphically, OK it's not the best trend in the world but we can see that our general trend is that as engine coolant temperature drops, our idle speed or throttle position target increases.
32:54 So what I would tend to do in this situation, let's say that 20° is the first point that we get to tune, I would tend to extrapolate the trend that we're seeing and move that out into the areas that I can't access.
33:11 Now again this might not give us the perfect results but it's likely to get us very close and when I was running a professional tuning workshop and we were tuning cars in the middle of summer I would always tell the customer, hey look if you find that in the middle of winter your cold start or idle speed control isn't perfect, feel free to come back and leave the car with us for a couple of days and we'll happily touch up that area of the tune.
33:37 Now for me that's not a lot of work when the car comes back, I'll have a look at it, it takes perhaps 5 or 10 minutes of my time but what it also does is if you're tuning for customers as opposed to for your own use, it already prepares the customer that hey, in winter we may find that everything isn't quite as perfect as it is now, and that way they're already prepared for that, they know what to expect, they know what to do if there is a problem and they're going to quite happily bring the car back and allow you to fix that as opposed to perhaps telling people that they know that you don't know what you're doing.
34:12 So we can only do what we can given the situation we have available to tune the car in.
34:18 So yeah short story there is extrapolate the trend that we're seeing in this graph out into the areas that we aren't able to access.
34:28 OK so at this point we've got our base table tuned in open loop, both at our normal operating temperature and then also at our colder temperatures as well.
34:40 So remember at this point we still haven't enabled our closed loop control.
34:46 I said there were two ways of tuning this base table though.
34:51 The other way we can tune this is to enable our closed loop control and then use the values that the ECU is calculating to populate this table.
35:03 What I mean by that is if we enable closed loop control and for example with our throttle our e throttle control here, the idle speed is lower than our target down at these lower engine coolant temperatures.
35:17 What we can do is watch our throttle position value here and this is going to be the result of the closed loop control and once our idle speed matches our target, we can populate our base table with values from this throttle position.
35:34 Now I will just point out that in this case, the total value, the final value of our throttle position main value that we're looking at here is the result of our base table, so this table here, plus the e throttle target table values that we've already looked at.
35:59 So that's a little bit of a trick here.
36:01 If we simply took the value from our throttle position live value and we entered that into our base table, that is not going to give us realistic values.
36:12 If on the other hand, we're using a solenoid or a stepper motor for our idle speed control, this is actually a lot easier.
36:20 What we can do is press R or F12 to bring up our run time values and if we click on our auxiliary functions we can see down in the left hand corner here we have a lot of information relating to our idle speed control.
36:37 So for example here we have our idle speed target, have our idle speed target.
36:42 We also have this status of the idle speed control system so we can see if the system is increasing or decreasing our idle speed control in order to match target.
36:52 And if we're using a solenoid or a stepper motor, we'll be able to see the position being displayed here so we can use this information to help us populate this base table so in this case, we're actually letting the closed loop control system do a lot of the hard work for us and then we're going to simply come in behind it and copy that data into our open loop or base position table so it's a really good way of fast tracking that tuning process.
37:23 OK so at this point we have our idle speed control functioning really nicely.
37:28 We've got stable idle speed control at our normal operating temperature and we should also have stable idle speed that's matching our target very closely right through the rev range.
37:40 Remembering at this point we would still be operating in open loop mode so we're still not really allowing the ECU to do anything to correct our idle speed control.
37:51 There's a couple of extra parameters that we can use now to help really fine tune that idle speed control and get the best results possible.
38:01 Let's just go back to our idle speed control.
38:06 And what we're going to look at is our idle up tables.
38:10 Actually let's go back to our idle speed control main.
38:13 We've already talked about this, we've got our engine, our engine fan, our power steer and our neutral park step values.
38:22 And what we want to do now, while we're still in open loop is tune each of these 3 parameters in order to maintain as close as we can to our target idle speed as the engine fan, our air conditioning, step in and out or if we're in an automatic transmission, as we step in and out of gear.
38:42 So the process for doing this is relatively straightforward.
38:46 When we're up to our operating temperature, we're going to obviously have our engine fan step in and out.
38:53 And as those fans step in and out, we can watch our idle speed control and we can adjust our engine fan step until we're getting really stable engine idle speed as the engine fans step in and out.
39:08 Now you can see in our 350z I'm using 0.5% step there to increase the throttle position when the engine fans turn on and off.
39:19 Next we can do exactly the same with our power steering.
39:22 So that just involves, we obviously need a power steer switch fitted to the vehicle to actually tell the ECU that we're using the power steer or there's some drain from the power steer system and again, we can just simply turn the steering wheel to load up the engine using the power steer pump and then adjust this value to get as close a control to our target idle speed as we can.
39:48 Lastly if we've got an automatic transmission, again we can go through that same process by simply putting the car, putting the transmission in and out of gear.
39:57 So these 3 parameters here, just help to improve the idle speed control and the stability of that as the load on the engine varies.
40:07 And again the closer we can get our idle speed control to our target in open loop, the better control we're going to have in closed loop 'cause the closed loop control system will have less work to do.
40:20 Next we can move down to our idle up tables so first of all we have an air conditioning step.
40:27 Now this particular car is no longer fitted with air conditioning but again this is really tuned in exactly the same way.
40:34 We simply want to turn our air conditioning on and off and as the air conditioning switches in, again it applies a mechanical load to the engine through the belt that drives the air con pump and we're just going to simply adjust our steps until that results in stable idle speed control.
40:53 This gives us the option of adjusting that step relative to our engine coolant temperature if we really want to fine tune that adjustment.
41:02 Let's go back and we also have a startup step table.
41:06 Now even with our idle speed control dialled in and really well tuned with the engine running, we'll also generally find that we're going to get an advantage in smooth idle speed control if we add an additional step up when we first crank and start the engine.
41:26 That's going to allow the engine to come up to normal idle speed really quickly and easily rather than stuttering, stumbling and running at a low idle speed initially so again we've got a 2D table that lets us adjust this relative to engine coolant temperature.
41:43 I will point out that this particular table needs to be tuned once our base table is completely tuned because this works on top of our base table.
41:54 So if we haven't properly tuned our base table, we can get into a weird situation where we're trying to account for inaccuracies in our base table with our startup step.
42:05 So we simply want to tune this so we get crisp, clean startup without the engine speed overshooting our target and without the engine running low and rough at a low idle speed for a few moments before our idle speed control system comes into play.
42:22 OK so that's dealt with our idle speed steps.
42:26 Now what we can do is go back and we're going to reenable our closed loop control and we can see how accurate and how effective that is.
42:35 So obviously at this point we should also have very little work for that system to do as I've mentioned.
42:42 Now there's one other aspect that I haven't talked about here and this is again only relevant if we're running in closed loop which is our deadband.
42:50 And simply this is the range of engine speeds around our target that the closed loop control system will accept as being on target.
43:03 So in this case you can see I've got that set to 25 RPM which is actually relatively tight for idle speed control.
43:09 So essentially what this is saying is if our target idle speed is 800 RPM, the ECU is going to do nothing in closed loop to adjust our idle speed control circuit if our engine speed happens to be between 780 RPM and 820 RPM.
43:28 Now we need to be again realistic with what we expect from our idle speed control circuit and the reason for this is it's a relatively slow moving control system as opposed to for example variable cam control or even boost control.
43:46 So if we're trying to have our deadband set very tight, it's going to give the control system a lot of work to do that's simply unnecessary and it's going to be fighting the natural fluctuations in engine speed that we're going to simply see in any engine.
44:02 OK so now that we've got our system set up and we know what we're trying to achieve and how to go about tuning this, we've got one more table that I want to just talk about which is our gain table here and I've clicked on our proportional gain and essentially this is the same as any proportional gain with a PID stye control algorithm and what this is going to do is control how aggressively the idle speed control circuit will chase our target idle speed.
44:36 Now if we've got the values in this table set too low, what we're going to see is errors between our target idle speed and our actual engine speed.
44:46 On the other hand if we've got the values set here too high, we're going to see instability in our idle speed control system and the idle speed or the engine speed may actually oscillate above and below our engine target idle speed so generally I've found that this table actually needs very little work in the G4+ and generally a value of somewhere between about 0.5 and about 1.5 I've found in all of the applications I've tuned on the G4+ has worked incredibly well so it's a table that you probably won't have to spend a lot of time on however if you're seeing instability in your idle speed control and oscillations as I've discussed, I would suggest coming back to this particular table and maybe making some adjustments.
45:38 If you're getting oscillations and instability, I would try starting by halving the values in the gains.
45:45 On the other hand, if you're getting really slow response, I would start by doubling the values in these gains and this is the same way I tune any PID system.
45:53 What I want to do is start by making quite an aggressive adjustment to the gain so that I can actually see the result of that change.
46:01 If we try making very small adjustments it's likely you're not going to see the effect of that change that you've just made.
46:07 By making a large change, by either doubling or halving the values, we're likely to see the result of that change and then we can assess based on the effect of the change, whether we've gone in the right way or we've gone the wrong way or maybe we've gone the right way but just perhaps a little bit too far, then you can start fine tuning that adjustment.
46:25 OK so right now I'm just going to actually, while I've been idling here we can see that our lambda is a little bit too lean.
46:34 This is another point here that we need to make sure that our engine is tuned relatively well in terms of our fuelling at idle speed.
46:45 If the target lambda that we're using, the measured lambda that we're using, at idle is really really rich or really really lean, that's also going to affect the idle speed control circuit's ability to do a really good job.
46:59 And as you can see as I richen the lambda there from about 1.1 which is where it was idling while I was talking, to lambda 1 right on our target right now, we actually saw that, if you were paying attention, the engine speed raised from about 780 RPM to 820 RPM so we actually switched from one side of our deadband to the other.
47:22 So it just shows you we've got a 40 RPM difference there based on the changes that I've made.
47:29 OK so the other aspect we want to always look at, it's not just enough to enable our closed loop control and assume that everything's going to be just fine, obviously as with any closed loop control system we also want to test and make sure that it is effective and what we want to do here is see how the idle speed control works as we actually drive the car, as we actually use the car and a quick test that I always like to do is just to bring the engine speed up and see what happens to our idle speed as we come back to idle.
48:05 And what we really want to do there is see the idle speed drop, the engine RPM drop back down to idle and sit at or very close to our idle speed.
48:15 I just logged what happened there so let's have a look at our idle speed and our results there.
48:21 So in our top log here, we have our engine speed as well as our idle speed target.
48:30 I've just zoomed in on this so we've got a really tight focus so we can see exactly what's going on.
48:36 So you can see I'm only spanning out to 1500 RPM here.
48:39 Next we've got our throttle position main so this shows what the actual throttle position is doing, you can see here, jumps off the scale as I have blipped the throttle and lastly we've also got our idle ignition control working here in conjunction with our idle speed control circuit in order to control our idle speed.
49:01 So what we can see here, the important part we're looking for is what happens when our engine RPM drops back down? So you can see in this instance, we have actually had the engine speed drop down slightly below our target, we've dropped down about 80 or 100 RPM below our target.
49:19 That's generally pretty normal, we're not going to always be able to achieve a perfect result where our engine RPM drops bang on, sits on our idle target.
49:32 There is always some response time or delay with this system and as I've said, idle speed in particular is a relatively slow moving system.
49:42 And what we can see here as well, we can also monitor and see what both our throttle position as well as our idle ignition control are doing in order to correct that error and you can see that the idle speed control comes up and very quickly settles at our target.
49:59 Now if we're seeing that our idle speed is dropping significantly below our target though, what we can do is go back to our idle base and we can try increasing our base value at that particular point.
50:17 So I've just added 0.4% in the area we're operating at.
50:22 Let's just log that again.
50:25 So I'll do exactly the same, just blip the throttle, allow the engine to come back down to idle and we'll just stop our logger.
50:33 And we can see that we've still got the idle speed drop, the idle speed has dropped below our target but you can see that that is also reduced.
50:42 However, the flipside of this is now you can see that we're actually sitting a little bit above our target idle speed once we were back into operation so we do need to balance this, if we increase our base value too far, we may find that we can't actually reduce the idle speed down to match our target.
51:04 OK I'm going to jump into some questions and answers really shortly so if you do have any questions that you want to ask about this, please put those into the chat box now and I'll deal with those very shortly.
51:18 But just to recap the general procedure that I like to go through, it's always good if we've got an idea of the procedure in mind so we know a step by step process we can go through, make sure that we're going to get the right results and we're not going to end up overlooking anything critical.
51:36 So my own process is to start the tuning process in open loop mode.
51:40 So we don't really want the closed loop system to be making up for any errors.
51:46 What we're going to do is start by tuning that base table at our normal operating temperature.
51:54 And remember we want to make sure that our fuelling is correct in those areas.
51:58 We can then repeat the process from a cold start, we want to tune our base position table as we warm the engine up so every step of that table we want to make sure that we're sitting at our target idle speed.
52:13 Next we can deal with any idle up tables for air conditioning, for our engine fan, power steering and our neutral drive switch as required and once we've got to this point, we've got an open loop control system that should be giving us really really good results even without the ECU doing anything to help the system there.
52:39 Once we've got this situation achieved then we can enable our closed loop control system and we want to fine tune that system as required, we may find that we still need to make small adjustments to our base position table and alternatively we may also find that we need to make adjustments to our gain table.
52:59 If we've gone through that procedure, we should have a closed loop control system that's going to be incredibly effective and give us that OE like control of our idle speed.
53:11 Just about regardless of the engine's operating conditions.
53:16 And that's going to mean that our car's not going to stall, it's not going to flare up and sit way above our idle speed target and it's going to do everything that we would expect from a factory off the showroom floor, a factory car.
53:31 Now remember tips there as well is we can use our data logging for looking at how the idle speed control system is functioning and particularly for solenoid or stepper motor, the run time values give you a guide to see what's going on there as well.
53:50 OK I'll jump into our questions and we'll see what we've got there.
53:56 Dave Creedman's just made a point there, I'll just read this out.
53:59 Dave said I wanted to make a point that's commonly overlooked, especially on cars that have been worked on by other workshops, or have a new combination of throttle body intake manifold or camshaft swaps.
54:12 I personally disable all idle control devices excluding drive by wire and set the mechanical throttle blade air gap, making sure the engine is warmed up and idle ignition table is correct.
54:24 Adjust the throttle blade air gap to achieve close to the desired base idle speed within perhaps 100 or 200 RPM then make sure you do a TPS calibration and restart the engine and check how it idles.
54:36 Doing this procedure minimises the time taken to correct idle issues and also gives you accurate control.
54:43 Yeah look that's a really great point that Dave's made there.
54:47 Basically what he's talking about there is setting the throttle stop for a mechanical throttle body so that we're already close to our normal hot operating temperature idle speed and that's going to give that idle speed control circuit less work to do so yeah that's a really good point there Dave, thanks for mentioning that.
55:10 Looks like we haven't got any other questions there.
55:13 As usual, if you do have any questions that crop up after this webinar, please ask them in the forum and I'll be happy to answer them there.
55:21 And we look forward to seeing you all next time, thanks for joining us.