My 2001 C240 has decided it wants to idle rather roughly. I've had into the stealer twice, unfortunately, since I was too buried to look at it. The first time they said it was probably the Harmonic balancer or the engine mounts. Nope it wasn't. I then took it in again after a couple of weeks and the next mechanic said it was the ignition wires. I then took it to my buddy, who has 20 years of working on MBZ's and Porsche's. He put the scope on it and he said that wasn't it either.

It runs perfectly at speed, and it doesn't idle roughly all the time.

Any ideas?

did the problem start shortly after a new tank of gas, with the petroleum situation presently a tank of bad gas could be a real possibility

Nothing related to gas that I can find. Fill up neither makes it better or worse. This has been going on for two months.

Mine is doing the same. Its a very slight rough idle mostly felt while in D.

Let me or us know if you come up with the resolution first.

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99 C43
98 S420
99 C230K
01 C240

I've experienced a similar problem with a W203 C240- rough idle, worsens with A/C on, and this condition deteriorated with time (~1 year) to include a very apparent loss of power.

The car's been to the dealership a number of times, they've been good at goodwill-ing some service, but the problem is still there. They've replaced:

O2 sensor
plug wire sets + coil packs
plugs ($100 in just plugs!?!)
MAF
Air filter

Additionally, they've performed a compression test, computer diagnostic, adaptation, code scan...and still have not been able to fully resolve the problem.

All the work has smoothed out the idle somewhat, but loss of power is still there. It has been recommended that I try swapping the ECU, or that a glitch may exist in something emissions related. But that's an expensive gamble that may or may not fix the problem.

Sorry for the rant, hope someone figures out why this is happening.