94 SL500 Rough Idle

[GeorgeH]

A few days before getting the 60K service, I had my engine steam cleaned. When I drove it off, it seemed to be missing badly. About 5 mins later it stalled. It started again and seemed to be fine. However, even after the 60K service, I notice that I have a low level engine vibration where it seems like the engine is missing occasionally. The whole car shakes gently when it happens. I suspect it's one cylinder. It seems to be worse when it cold or damp outside. The spark plugs, caps and rotors have been replaced, and I have new engine mounts. Any ideas of what might be causing the misfiring/vibration?

[deanyel]

Are you able to pull fault codes? That would tell you right away if you have any ignition issues. I once had a motor mount fail within minutes of installation, fluid just leaked out. I was so unsuspecting that it took months to find. But it sounds like yours is more intermitant than that. I would start with fault codes - if you don't have a code reader do a search for Arthur Dalton's fault code reader. You have a 38 pin diagnostic connector.

[GeorgeH]

I took the car to the dealer again today and happened to run into the shop foreman. He took a look at the problem and determined that at least one of the new motor mounts are bad, as the engine lifts up when it's rev'ed up.... so much so that the air intake pipes move about 3/4s of an inch. If this turns out to be the problem, it's amazing just how much vibration the mounts shield.