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Hi guys,

Should the idle characteristics of my car change when I move the TPS? 

On my E32 735i when I moved this it had a definite effect on the engine idle.



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Yes I would expect it would. The spark map will vary the ignition advance depending how open the throttle is. And varying the advance will vary idle speed.


(based on general knowledge - I know nothing about your model!)


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Hi Al,


Just been playing in this very area on my Diamantschwartz eta.


The warm idle was erratic and very lumpy, while on throttle drive ability was unaffected.


The throttle body should have a 0.015" clearance between the throttle body and the throttle plate, which is adjustable via an external adjustment screw covered by an anti-tamper cover.  This should allow some air flow past the throttle plate at idle.  My plate had worn so as to be shut which contributed to the erratic idle as the idle control valve is unable to respond fast enough without this air leakage path.


In addition, my throttle position switch had also worn and was not indicating closed when the throttle was closed which further contributed to the erratic idle issue.  As a "get by" I had to elongate the switch adjustment slots for the mounting screws so that I could set the switch to indicate shut when the throttle is shut.  The switch is also full of oil from the throttle body. 


This is very easy to set up and test with the throttle body off of the car.


In summary the throttle plate position and throttle switch position have to be set correctly and be in agreement otherwise it confuses the sh1t out of the engine management system.


The Bentley manual has all the clearances, ohmic values, voltage values that assisted with diagnosis and resolution.


My idle post resolution is now around 850 rpm and quite a lot smoother.


Now need to source a new throttle body and throttle position switch.  Might be prudent to acquire an idle control valve and air flow meter as well.


I was fortunate to have the Zobelbraun Eta available to conduct side-by-side comparison / diagnosis.


My systems run motoronic 1.1,  on an M20 engine whereas yours is an earlier M30 engine.  The relationship between throttle plate and throttle switch should be broadly similar in that when the plate is closed the switch should indicate closed to the control system.


Hope this helps.


Enjoy your weekend.






Edited by Ordnator

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Thanks Mick. I’ve suspected for a wee while that I need my TB cleaned out and recalibrated. 

My car is running at 95-97% perfect but that last 5% is bloody annoying. 

Think I need to get the injectors looked at too.  

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