Intermittant rough idle '95 S320
 

This occurs sometimes after driving for over 20 minutes.Engine starts to idle rough with a little surge. Shifting to N and and bumping up idle engine runs fine. In gear, with A/c on it's worse. After stumble on accel it smooths out and seems OK, but seems to lose power requiring more throttle especially on hills. This does not occur at all times,weather doesn't make a difference. I just had a $2000 bill for inspection (Pa.)and wasn't expecting to put more in right now. Is it an emission related problem ? The exhaust sound changes when this happens and the engine labors at idle. And the kicker is that if you stop to shop, dinner,visit friends, it may not reappear ! I heard of cleaning an EPR port ,but haven't been able to find a thread or link. Need some help....Thanks

Sorry, meant EGR port..Gerry

For starters , make sure you have F8DC4 plugs in there and change the 3 plug connectors under the coils

could be an engine wiring harness problem. I had to replace my harness off 1994 S320 with 135k miles. All of a sudden out of the blue it started misfiring like crazy. Someone suggested to replace the crank angle sensor. That cost me $120 and didnt make a difference.

I had an intermittant problem like that too (95 S320). I replaced the coils, plugs and wires. It's great now.

Good luck.

intermittant rough idel fix - W210
 

Gerry,

My 2002 E320 displayed similar behavior. The dealer couldn't fine the problem. I switched to an indy, who found that one of the two No. 6 spark plug wires was bad. No more problems.

Good luck,

Steve

Thanks to everyone for the suggestions ..have used the car the last 4-5 days and no problems ...GerryL

If you haven't change the wire harness yet, you will need to.

Note; Put a OBDII tester on, Showed 3 codes; Multi misfire, #1 Misfire, #5 misfire. Checked wires and the only place they meet is at a retaining clip.Insulated w/ electrical tape ,but will replace sparkplugs and wire harness. Thanks again for all the suggestions. It seems this is a weak point in the system that hasn't improved with newer models. FYI ; dealer price for identical Bosch wire harness is over $150 + installation. It is a very simple task to replace.

http://catalog.worldpac.com/mercedesshop/sophio/image.jsp?title=Spark%20Plug%20Connector&url=http%3A//img.eautopartscatalog.com/live/F101084561BER.JPG

This is the weak point on 104 Waste Spark ignitions.
Change them under each coil. [ 3 total]

Re-read post # 3.