I couldn't see how a fuel pump relay would cause a rough idle, but hey It's worth a shot. Yesterday I swapped the fuel pump relay out of an 87 300E I have, with the one in the rough idling 88 300SEL. Sad to say, it made no difference.

Peter

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Auto Zentral Ltd.

Sorry -- I may have been unclear -- I suspected that my older aftermarket relay was getting HOT and opening a circuit inside causing INTERMITTENT pump failure. My idle was very poor and stumbling [nonexistent at times when the car would not run (~_-)] but not all the time.

It's been a few days. Car has not died in the road and hot restarts are functional. Intermittent idle stumbles are gone.

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David
1986 300E Anthracite + ECodes + MB Mileage Award

I had a problem with the FPR getting hot and stalling the engine. After it cooled off it was O.K. So I replaced the FPR. All was well for about two weeks and it started doing it again. I ckecked the amp draw on my fuel pumps and one of them was way high. That was what was causing my sympton of a bad FPR. I replaced the pump and that problem went away.

Wow, thank you very much!

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David
1986 300E Anthracite + ECodes + MB Mileage Award