2002 W203 C240 idle problem...
A friend of mine brought his 2002 C240 over today. He's stumped. The car has an occasional rough idle. I experienced it. It sits, smooth, and then suddenly the idle falls below 500, and feels like the motor mounts have given out. It's rough, and stays that way for some time. Then, it returns to normal.
He's taken it to the dealer over and over again, and they ignore it. There's no MIL or anything showing on "malfunction" screen. No codes...
It really feels like it's going to stall. I've had a few C240 loaner cars, and none of them felt like this. I called my aunt, as she has a C240, and she's never had this problem.
If it were misfiring, you'd think it would record a code.
He's hoping to get some sort of info to take with him on his next dealer visit.
1998 C230 "Black Betty"