Mercedes 420 sel

MADOC

MEMBER
1989 MERCEDES BENZ 420SEL
6 CYL
2WD
AUTOMATIC
198,000 MILES

My car is idling rough and occaisionally skips while driving

Saturday, January 29th, 2011 AT 4:48 PM

2 Replies

RASMATAZ

MECHANIC
75,992 POSTS

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

https://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-

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Wednesday, March 16th, 2011 AT 3:14 AM

GEORGE WITTENBERG

MEMBER
1 POST

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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Saturday, October 29th, 2011 AT 11:45 PM