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MikeJ 6/24/2010

1987 Mercedes Benz 300D Base 6 Cyl 3.0L


What would cause the car to run rough until warmed to normal driving temperature?

On cold start, car runs rough, lots of smoke out the exhaust, but smooths out and runs great after engine warmup. Have replaced both fuel filters, glow plugs, all fuel injectors and the washers on the injector pump nozzles. Have checked for air leaks on the injector lines.

1 Answer


tomclark88 2/25/2013

did you check the glow plug relay? when you turn on the key, does the yellow glow plug light come on for a few seconds and go off or does the light come on after the engine starts? if its coming on after the engine starts it could be a bad glow plug (yes, you can get a bad one so you should check them again) or the relay may be malfunctioning not allowing the glow plugs to get hot enough.


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