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Practical Standalone Tuning: Step 6: Idle Tuning

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Step 6: Idle Tuning


00:00 - Once we've got the engine running, one of the first jobs we need to do, is set up the idle speed and idle speed control.
00:07 Make sure that we can actually make the engine idle properly by itself.
00:11 And this is an area we can quite often pick up problems.
00:15 Basically if you can't make the engine idle by itself at a realistic and reasonable RPM, it could be the indication that there's something else wrong mechanically, and it can save you a lot of time working that out, figuring that out now, rather than jumping on the dyno, and wondering why the engine won't tune up properly and why you can't get the power you'd expect.
00:35 So again in this particular car, it's basically completely standard, the engine's never been apart, and the ECU again comes with a really good configuration for our idle speed control.
00:46 So there isn't a lot of work for us to do, but I do want to show you what the adjustments are and how they can be made.
00:53 Now again this particular system uses the electronic throttle body to control idle speed.
01:00 Doesn't really matter what system you're using.
01:03 It's the principal that really counts.
01:05 So we're going to show you what that is now.
01:08 So the first place we want to start is with the aim idle.
01:12 So this is a table of target idle speed versus engine coolant temperature.
01:17 And you can see that basically down at 20 degrees and below, we've got a target idle speed of 1100 RPM.
01:25 Once we get up to 80 degrees and above, we're targeting an idle speed of 800 RPM.
01:30 And we've got this smooth sort of linearisation between those two points.
01:35 The actual idle speed your engine's going to be happy with will depend a little bit on your engine.
01:41 If you've got an engine that's got really aggressive cams with a lot of overlap, you're going to have to pick up that idle speed quite a bit to make the engine run properly.
01:51 And that's one of the most common mistakes I see, is people struggling to try and make an engine idle at an unrealistically low RPM.
01:59 So again this engine's completely standard.
02:01 We know it's going to run really happily at 800 RPM idle.
02:05 Even lower probably if we wanted to.
02:08 So once we've got that table set up, that's our first point.
02:11 Then what we would do is we would disable any closed loop control that the ECU has.
02:16 So basically that means the ECU's not trying to make changes to the throttle body opening to achieve that idle speed.
02:25 Then we can move on to in the M150, the idle actuator setup table.
02:31 Now this has a lot of settings here for basically where the throttle body will be held, or how much air flow will be provided.
02:40 In this table here we've got a 3D table of throttle body opening.
02:47 Or in this case it's called idle mass flow feed forward.
02:51 So it's the idle mass flow versus our idle RPM and also our coolant temperature.
02:58 So basically by increasing these numbers, it will increase the air flow basically the throttle body opening, and it will increase the idle speed.
03:08 So you can see there if we do that, our idle speed will increase.
03:14 And if we drop it down to 30, and we look back at our tuning page, now we're idling down at 700 RPM.
03:25 So that's basically what that setting does.
03:29 It is quite time consuming to adjust and set this up.
03:35 We've got our target idle speed here in this graph, versus our engine speed.
03:40 And what we wanna do is basically rev the engine and make sure that the engine RPM is dropping down smoothly to our target idle speed.
03:50 If this table here is set too high, what will happen is that the engine RPM will hang above our target, and it will never drop down to our idle speed.
03:58 If on the other hand it's set too low, what will happen is our idle speed will be low, you can see here we're tracking below target.
04:05 And particularly if we rev the engine, what will happen is the engine RPM will drop down, and if it's too low that'll end up with it stalling.
04:15 So it's quite time consuming to set this particular table and it needs to be done at a variety of coolant temperatures to really fill in the table properly.
04:22 Once we've got that table set up and the engine is idling smoothly, at that point you can reintroduce the closed loop control and let the ECU take care of any discrepancy between your target and actual idle speed.