Rough iddle
 

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

Fuel filter? when was that replaced last?:confused:
At what point it has symptoms? All the time, when hot, etc.

the coil does effect this but there's also a lot of different sources also. Have you checked your wires/wire ends,cap, rotor,etc? I've also had this problem and just changed my coil this past weekend (just because I noticed on the paperwork that came with the car that a previous printout from a service done on it noted that the coil was "weak" and had a slight miss/bump at idle) and it smoothed out and throttle response was great initially up until like Tuesday when it went back to its old ways. It then ran perfectly again for another couple of days until it kinda resembled the symptoms a little bit this morning. I'm also gonna replace my new wires when they get here and my cap, rotor and see what happens. Good Luck

Alan

P.S. My search for a new bosch coil found fluctuations in price from about $115.00 at some places up to over $200 at the Dealer. I ended up with a great deal from N.O.P.I. aouto parts store here in Atlanta who ordered the same coil directly from bosch for $80 and just charged me $4 for the shipping in 2 days! So shop around;)

A suggestion
 

Check your plugs and wires. This is a common symptom of a misfire. When replacing plugs it is easy to crack the ceramic. Over time, the plug will begin to arc. It won't necessarily happen on every rotation, just intermittently. It also won't be noticeable on acceleration.