MERCEDES 420 SEL

1989 Mercedes Benz 420sel

Tiny

Madoc

January, 29, 2011 AT 4:48 PM

My car is idling rough and occaisionally skips while driving

FOUND 4235 RELATED QUESTIONS

Running Rough

27 ANSWERS
34 IMAGES

Idles Rough/changed Ects

37 ANSWERS
3 IMAGES

2 Answers

Tiny

rasmataz

March, 16, 2011 AT 3:14 AM

Engine running rough or misfiring can be cause by the following:

http://www.2carpros.com/articles/engine-misfires-or-runs-rough

1.Defective spark plugs
2.Inadequate spark/coil,defective spark plug wire.
3.Lack of compression
4.False air leakage.
5.Faulty fuel injectors.
6.Insufficient fuel pressure.
7.Contaminated fuel.
8.EGR valve that is leaking.
9.Oxygen sensors.
10.Throttle position sensor.
11.Manifold absolute pressure sensor
12.Mass Airflow Sensor
13.Idle air control valve

Note: If it doesn't apply disregard it-

Tiny

George Wittenberg

October, 29, 2011 AT 11:45 PM

I've had the same problem and had a lot of work done, including replacing injectors, plugs, oxygen sensors, etc. The rough idle continued until I studied the repair manual and discovered the idle control valve. For a car this old, it was never replaced. I ran down to AutoZone and bought a new one with warranty and replace it. The rough idle immediately disappeared and the engine is so quite know at idle, I hardly notice it. This may not be your problem, but the fact that you have an 89 and have tried other things points to it Generally owners neglect this inexpensive part after many miles of driving.

George

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