Thread: W203 engine idling problem

Hi MB GURU,
I have a 2002 W203 C230K sports coupe, when the engine is warmed up then the idling refs are fluxuating between 1000-2000rpms but when i put the AC on then the idling returns to normal? Any suggestions?

Sounds like you have excessive resistance on the AC pump or you have a vacuumn leak.

Idle hunting is a symptom of M111 based engines and it is a problem associated with failing wiring insulation, vacuun leaks or excessive resistance in one of the sensors.

I used to have this problem and when I did some changes to my cars wiring the problem vanished. The one thing that seemed to fix it was that I removed the electrical vacuum assist pump and changed it to the mechanical version attached to the cam. I also repaired and replaced all of my main and minor vacuum lines.

This boosted brake pedal feel and stopped the "hunting" you are getting. It needs to be checked carefully. No one answer is the solution.

Thanks for the reply, the guys at my MB service centre told me that there's oil in the wiring harnass and it's also making alot of errors to apprear ! Must i now replace the whole harnass or isnt there some other alternative??

In this particular car the harness is known to be heat affected and the insulation fails. In some cases the harness rubs on the engine. The cam adjuster in the front of the engine can also percolate oil into the engine wiring and all of the sensors - including the engine controller.

I have seen engine controllers full of oil. Total damage was 3 modules and 1 wiring harness.

Install the cam adjuster spacer with A271 part number.

Damn, now i wonder why i pay those guys at MB service centre so much money, cause they looked clueless ! Thanks again for the advise and i will make sure they install the spacer