1990 560 sec rough idle I have tried it all with no luck! Help!! - Mercedes-Benz Forum

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post #1 of 2 (permalink) Old 05-15-2011, 06:01 PM Thread Starter
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1990 560 sec rough idle I have tried it all with no luck! Help!!

Hello to everyone,

I am trying to help a friend of mine with their car. It is a 1990 560 sec with 121,000 miles and it has a very rough idle however as soon as you give it the gas it picks up and runs strong. I am new to the forum but have followed posts on it since I was asked to help with the car more than a year ago. So far I have replaced: spark plugs, wires, cap rotor, fuel infector seals, air breather hose and some vacuum hoses. Everything that I have done has not changed how the car runs. It has been taken to a mercedes dealership to have it looked at, they checked the compression and looked into the timing chain and they said all appear to be in good shape but can not figure out the problem either. when in drive it seems like it is missing on two or three cylinders. It idles around 500 rpm in drive but tends to fluctuate from ~600-1000 rpm in neutral. I have also noticed that when it is running and i push very slightly down on the flap in front of the fuel distributer it tends to start to smooth out and the idle picks up some. I have been trying to help my friend out for bout a year now with her car but I am completely stuck now. I do not want to admit defeat with it so I have come to ask for some help from the experts. What could it be and what should I check for next. Any help that can be given will be GREATLY appreciated!
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post #2 of 2 (permalink) Old 05-15-2011, 07:18 PM
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Try asking in the cars designated forum. You will probably recieve more specific answers there.
W126 S,SE,SEC,SEL,SD,SDL Class - Benzworld.org - Mercedes-Benz Discussion Forum

Have you replaced the fuel filters?

1979 Pontiac Firebird 5.7- 86,142 miles
1981 Chevrolet Corvette 5.7
1984 Mercedes 190D 2.2 Auto - 140,628 miles
1987 Chevrolet Sprint 1.0 - 139,000 miles
1989 Oldsmobile Cutlass Calais S - 123,000 miles
1989 Chrysler New Yorker - 95,000 miles
1991 Dodge Stealth R/T - 101,000 miles
1999 Dodge Durango - 178,000 miles
2003 Dodge Dakota - 203,000 miles
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