slightly "rough" idle on C280

[leonb]

I have a 1999 C280 (V6) which idles slightly rough. Its not a constant rough idle. It will idle smoothly for say about 5 sec and then it will shake slightly- idle smooth, then shake. The rev counter only moves slightly, maybe 100 RPM, if than much - but it definately does have movement.

I already replaced the MAF sensor, due to stalling problems. The Benz technicians also say the car does not give any fault codes. They suggest either new plugs, or engine mounts. I don't really have confidence in their abilities and dont want to replace something if it wont cure the problem (already done to much of that)

Any suggestions??

I do have some question for the guru's:

1) Can it be motor mounts if the rev needle moves slightly during the "rough" idling?
2) If the problem is spark plug related, shouldn't it give an error code?

Something else: it does not make a difference whether the transmission is in P,N or D.

Thanks for helping