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Link G4 Plus Software Tutorial: Idle Speed Control

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Idle Speed Control

06.44

00:00 - Idle speed control is essential if you want an engine that will start and run smoothly and hold a stable idle speed regardless of engine temperature and electrical loads.
00:10 There are a range of idle speed control systems from solenoids and stepper motors through to e-throttle.
00:17 You will need a suitable system fitted and wired in order to use the idle speed control function.
00:22 The idle speed control parameters can be accessed by opening the ECU settings menu and clicking on idle speed control.
00:30 To begin, we want to click on the idle speed control option which will open the main setup screen.
00:35 The first option we have is the ISC mode.
00:38 This will depend on the method you are using to control idle speed.
00:42 These are separated into solenoid and stepper motor or e-throttle.
00:47 For each option you can select open loop where the ECU will not make corrections to the idle speed output, or closed loop where the ECU will adjust the output to try and achieve your target idle speed.
00:59 Closed loop control is usually preferred as this gives the most stable control.
01:03 On some heavily modified engines, particularly those with aggressive cams, closed loop control will result in excessive hunting and stalling.
01:11 In this situation, open loop control can give a better result.
01:15 For this example we're going to set up closed loop control using a stepper motor so we can select the closed loop solenoid stepper option.
01:26 Next we have the speed lock out option.
01:28 This is only available in closed loop mode and can be used to prevent the ECU attempting to reduce or control idle speed during normal driving.
01:37 We can select off to disable the function or driven or non driven wheel speed.
01:42 To use this function you will need a speed sensor installed and correctly configured to match.
01:48 Deadband is used in closed loop mode and defines the range above and below the target idle speed that the ECU will accept as within range.
01:57 This prevents the ISC control system needlessly chasing tiny fluctuations in RPM.
02:02 Decel timeout is used to smooth the transition between the engine decelerating and entering closed loop control.
02:09 This holds the ISC system at the base opening position for the timeout period before closed loop control begins.
02:16 This prevents the ISC control trying to reduce the idle speed when the engine RPM first reaches the RPM lockout range.
02:24 Max and min clamp set the range of control that the idle stepper or solenoid will accept.
02:30 This can be used to limit the control range of the ECU.
02:34 FP/TP lockout is used to prevent the ECU attempting to control idle speed when the car is actually being driven.
02:42 Usually a value of 0.5 to 1% is typical here.
02:47 the RPM lockout function sets the RPM range above the target idle speed that closed loop control will be disabled.
02:54 This prevents the ISC control system ending up fully closed while the engine is in overrun.
03:00 This can help prevent stalling.
03:02 Lastly we can program an engine fan step and power steer step which increases the idle speed to cope with the extra load when the engine fan or power steering are active.
03:13 Once these parameters are set correctly, there are a few more tables that we need to set.
03:18 The first one to adjust is the idle RPM table.
03:22 This 2D table sets our desired idle speed relative to engine temperature.
03:27 It's normal for the engine to idle slightly higher when it's cold and reduce as it reaches operating temperature.
03:34 This needs to be adjusted to suit your engine.
03:37 Once this table is configured, we can adjust the idle base position table.
03:42 This is a 2D table of idle position versus engine temperature.
03:46 This table is where the ECU will set the idle stepper opening before it enters closed loop control.
03:54 It needs to be adjusted at each engine temperature zone so that the engine will idle properly.
03:59 If the base position is too high, the engine RPM will flare above the target idle speed, while if the base position is too low, the engine may stall.
04:08 A tip to setting this table is to use the run time values screen and click on the auxiliary tab.
04:13 On the left under idle speed, you can see the actual idle position that the ECU is supplying as well as the idle status.
04:21 This will tell you when the engine is at idle target.
04:25 When the engine is idling at the target idle speed, you can copy the current idle position and enter it into the base table.
04:32 This needs to be done at each engine temperature cell so we would normally start with a cold engine and do this at each cell until the engine is at operating temperature.
04:42 There are two more tables that you may need to make adjustments to and these are the AC step and startup step tables.
04:49 Both are 2D tables relative to engine temperature.
04:53 The AC step table increases idle speed to cope with the increased load when the aircon turns on.
04:59 This requires an auxiliary output configured as AC clutch and a digital input configured as AC in.
05:06 The startup step table offers an increase in ISC opening during startup.
05:11 This can be used to help achieve a stable idle speed immediately after startup.
05:17 Lastly there are three tables available to define how the ISC system will respond to errors in idle speed.
05:24 These are the proportional gain, derivative gain and anti stall gain tables.
05:30 Generally the default values work well and shouldn't need adjustment.
05:35 The proportional gain defines how aggressively the ECU will respond to an error in target idle speed.
05:41 The larger the proportional gain, the faster the ECU will try and drive the idle speed towards the target.
05:48 Too much proportional gain can lead to hunting or oscillating in idle speed.
05:52 While too little can result in slow response to an error in idle speed.
05:57 The derivative gain looks at how quickly the idle speed error is changing.
06:01 This is used to slow the response of the ISC control system and help prevent oscillating.
06:08 If the derivative gain is too low the idle speed may overshoot or oscillate.
06:13 If the derivative gain is too high the idle speed may be slow to respond and not meet the target.
06:19 The anti stall gain can help prevent stalling if the idle speed drops too low.
06:24 This provides additional ISC opening if the RPM falls more than 150 below the target.
06:30 If the anti stall gain is too high, the idle speed may increase sharply when the engine speed drops.