I plan on taking my car to the dealer, however I'm wondering what the opinions could be with this problem.

Problem: Engine in drive it has a rough idle, rpms seem to be at 600 rpm while in drive and idle, and seem to drop just a hair. The engine is always running rough in drive idle. However when it's in reverse gear it idles smooth. When I drive it, the engine runs smooth. I changed the spark plugs and tested each wire with an ohm meter, it didn't change a thing. What puzzles me is in reverse idle is smooth and not in drive idle.

other information, 1999 CLK430 with 158,000 miles.

any thoughts?

 

lt could be motor mounts ( very common to go bad or just wear out over time). put car in drive and hold the brake and blip the gas to see if the motor raises up on the driver side and in reverse it will raise on the passenger side usually the driver side mount goes bad.should only raise about maybe an inch or 2 movement. could be a bad transmission mount usually youll feel engine vibration in the seats. is the problem vibration or misfire

 

At idle it feels like a misfire, but was engine speed increases it smooths out. Wouldn't you notice the misfire in reverse gear? In reverse it's as smooth as glass. Thanks.

 

should make no differnce at all. thats why i was thinking maybe the motor mounts are worn out.

 

Did you discover the actual cause of your problem yet??

I have an almost identical problem with my 99 C230K. It is very rough and throaty sounding in Drive, not just at idle, though. But in Park, smooth as ever, and in Reverse, same thing, smooth and quiet. The rough sound and vibration in drive does seem to diminish on warm days. Seems like maybe some vacuum leak when in drive or something. Maybe some sort of temperature dependent valve???

Any suggestions, highly appreciated!