I am a newbie, with a problem that is difficult to diagnose.
I have a C220(1995) with 240K-mileage. Recently, it has developped an irregular rough iddle. Car will start without problem, driving with normal acceleration, etc. However, chronically it will act as if not all cylinders are firing properly- rough iddle, surging RPM, etc. Put the car in park - condition continues. Turn engine off and restart - everything seems to reset and runs smoothly.
I though it might be the injectors, but cleaned them up with a liquid treatment. Took the car out for a long highway drive (1000KM).
A friend suggested that it might be an "engine coil" which needs to be replaced. IS this possible? What does it entail? Cost?
Any suggestions would be appreciated. Thanks