Does it vibrate, or is it more like a misfire?
In my case, my first 240D (automatic) has a vibration (not a misfire) at idle that new motor-mounts and a valve-adjst didn't cure. Upping the idle speed slightly improved things in neutral. But in drive, the severe vibration continues. The PO's teenager had an accident in this car and some repairs weren't done well. The crossmember under the engine appears slightly bent and the left motor mount doesn't sit square. So I often shift into neutral at long traffic-lights. Otherwise, it drives OK for a $200 car, so I'll put up with the vibration till I sell it.

Happy Motoring, Mark

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DrDKW