Surging engine at idle HELP

[Ceeker]

most probably a secondary problem. sometimes one masks the other. T-state stuck open would just make the car run cool. temp gauge would be low. Clutch fan wouldn't engage properly. completely unrelated to engine revs moving up. the car even under cold start only increases engine revs slightly until the the car gets warm and the revs drop to normal 700prm. My car revs between 1600-2000k - with the car running rich. I suspect it's the AFM since when I unplug it the revs drop to normal with some sputtering to compensate for air/fuel adjustment. Car should stall when unplugged or very close to stalling. This isn't happening.

[TSI]

Fair enough. Assuming all vacuum lines are good, I'm out of ideas.

[RedEye]

Could be the coolant temp sensor (the one that feeds the ecu, not the gauge. The blue one iirc). After I fixed all my vacuum leaks the surging stopped but the car was running so rich it wouldn't warm start. The resistance of that sensor increases as temperature decreases; the sensor's internal resistance also increases with age and wear. So an aging sensor can be telling the ecu that the engine is a lot colder than it really is, hence running rich. When I got my car I think it was only running because the vast amount of unmetered air from the many vacuum leaks sort of balanced the vast amount of extra fuel from the dead CTS.

[Ceeker]

Originally Posted by RedEye

Could be the coolant temp sensor (the one that feeds the ecu, not the gauge. The blue one iirc). After I fixed all my vacuum leaks the surging stopped but the car was running so rich it wouldn't warm start. The resistance of that sensor increases as temperature decreases; the sensor's internal resistance also increases with age and wear. So an aging sensor can be telling the ecu that the engine is a lot colder than it really is, hence running rich. When I got my car I think it was only running because the vast amount of unmetered air from the many vacuum leaks sort of balanced the vast amount of extra fuel from the dead CTS.

I do remember swapping that some time back with a used one. that does seem to make sense. it is running rich for sure. Well, that may need swapping out for a new one. However, the sensor is brass and the only resistance it could bring with it is the tarnish? that can easily be cleaned up with a wire wheel. I think the sensor is like 15.00 -20.00 at most. Worth a try. thanks for the input.

[RedEye]

Cleaning didn't help mine, but yours might not be as far gone. I really hate working on engine electrical on these cars, the wiring seems so brittle with age I keep expecting the whole harness to shatter every time I touch it.

[Barry]

Well the surge is gone , now it just doesn't want to idle when it is cold. I have replaced the ICV and it made no difference. I have a code that read ICV. Check engine light is on except under heavy acceleration. then it feels like a little back fire and the light is on again.

So my question is could the throttle positioning switch be pouched??? I am really at wits end with this issue. Any thoughts would be appreciated.

[Dinanstu]

http://www.pelicanparts.com/bmw/tech...leshooting.htm

[Barry]

Thanks I will check the tps tomorrow

[Barry]

Throttle Positioning Switch is pouched. No continueity between 2 and 18

[Barry]

So I have replaced the TPS and I have a beautiful idle and responce from the engine. Why does the check engine light keep doing the on /off thing?????? This is behound frustrating. The code still reads ICV, could this be associated to the 02 sensor? I am reaching for anything at this point.

[Barry]

I took a stab in the dark and replaced the computer. Bingo light went out. Now I am getting a back fire once and awhile when I am coming off the gas, Check Engine light flickers. Any ideas what might cause that?????