Doug427

My 1998 C230 runs very smoothly when at any speed above idle, but idles fairly roughly, especially in drive when the RPM's are lower. No check engine light is on. Any common problem areas I should look at? I did remove and clean the throttle body (it was filthy). I also removed and sprayed the MAF sensor, which some around here where I live have told me is not usually a good idea. Too late, it's done. The cleaning of the throttle body did make a very small change for the better.

I have looked for vacuum leaks, but haven't seen anything obvious. What's the best trick for trying to pick up a vacuum leak that you may not have noticed?

Any other ideas would be greatly appreciated.

Thanks!

SlickVick

Do you have a check engine light or no?

Doug427

No check engine light. Car runs smooth except at idle. Not too bad in Park or Neutral, very rough in drive at idle.

PJmak

I have exactly the same thing on my 00 c280.

I got a check engine light for egr valve p0400

Im planning to look into that and also i heard ovp relay and voltage regulator could cause this.

any electrical issues with the car?

PJmak

Take your egr valve off. Its got a sensor attached to it and three rubber lines for vacuum. I had one line that was really bad(going into the intake manifold and around 4-5" long)

Another one that connects the sensor to the egr valve was not as bad but i replaced it too.

My idle improved dramatically but it still shakes. I think I might have bad engine mounts

Doug427

Just to report back. I changed both engine mounts and the trans mounts. Now smooth as silk. I've never seen a car before so sensitive to engine mounts. Live and learn, I guess.

Viktori

wrong thread