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Motronic expert needed

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Car is 535ise with Alpina cam and chip, Motronic 1.3


Problem - when warmed up the car wants to idle at 1200 rpm and is eager off idle to say the least.   Other than that it runs absolutely fine.


here is what I have done but to no avail.


1. New TPS, adjusted and confirmed correct signals back to ecu plug for idle and WOT.

2. New CTS, tested back to ecu and shows correct 300 ohms when warm

3. New idle control valve - confirmed operating 

4. No air leaks, new vacuum hoses, inlet gaskets etc.

5. Separately I had the throttle body bored out to 68mm, new spindle and throttle plate, fitted, adjusted to fully closed but still a high idle speed.  It had a high idle speed before this was done.

6.  I have an afr meter fitted (AEM) and idle air fuel ratio is set to 14.8 

I know the Alpina chip raises the idle speed to 950-1000 rpm

i also know that the ecu sets idle speed

The ecu seems to be requesting a high idle speed (as if it thinks it is a cold engine?) even though the CTS is telling it that it is fully warm, and TPS is closed.


i am running out of other things to check,  unless you guys can suggest some other things to look at.


thanks, Ian

Edited by M635uk

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Ok, I have the old idle control valve so could swap over.  It definitely feels like there is too much metered air getting in as it runs very smooth, just too high.  Especially as the throttle plate is new and definitely fully closed, so there isn’t any air getting past that, the only other route will be the icv or the bleed in the air flow meter for CO setting (but that is close to closed).   If I force the idle speed lower by riding the clutch it sometimes stays around 1000rpm...odd



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