I took it to mb dealer replaced distributor cap and plugs 565.00.I got 30 minutes away rough idle started again.Reluctant to take it back can't aford parts replacement diagnosis.Its an intermittent problem sometimes it idles smooth as silk other times it shakes all over the place. Any suggestions would be greatly appreciated.

Can you describe the rough idle? Is it a miss or a chassis vibration? Does it happen in N or P?

Its a miss,Happens in park or drive

Very likely a vacuum hose leak. Remove the air cleaner and check every hose and connection you can see. A leak will also show up if you take your propane torch (for soldering plumbing) and open the valve, wave the tip around near all injectors and hoses, listen for a change in engine speed....and no, it won't ignite even if you hold it next to the hottest part of the exhaust...but someone will probably flame-in here with a warning..
Another possible is oil or something fouling up a sparkplug. Remove and check all of them...could be that the problem has had enough time to re-foul one of them (in my case, I have a leaking valve stem seal in 1 cylinder, change that plug and it will eventually foul again and cause a miss).

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1986 560SL
2002 Toyota Camry
1993 Lexus

Just had the spark plugs changed.I will check for vacuum leaks.Would a vacum leak come and go.


Thanks for the reply.I'm a first time Mercedes owner and this forum has been an awesome source of info.

I don't know if this car is new to you or not, but my 90 300E had this problem when I first bought it. A bottle of injector cleaner and two full tanks of good quality 92 octane fuel got rid of it.

Mine was going into a rough idle about once per day. Sometimes at a light, sometimes when we stopped and let it idle, sometimes when we stopped and turned it off it would do it when we restarted it. In all cases, getting in the throttle once or twice seemed to clear it and then it would be fine until the next day. Actually the PO had told me about this, but figured it was just because his wife only drove the car to and from work, which was only about a mile and a half away. Could have been she put some cheap gas in it that caused the problem.

Anyway, if you just recently got the car you might want to try this route before you start pulling your hair out.