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?