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Old 07-17-2000, 12:14 AM
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I've just had a valve job done on my '77 280E and the car is now idling very badly. It doesn't appear to be the cam timing.

This morning, the power just died while I was going up a hill, to the point when the car stalled. But by the time the mechanic got there, it started fine.

They found that two of the six (new) plugs were totally clogged, and they suspect that a partly corroded warm-up governor is enriching the fuel too much, exacerbated by my frequent short trips to and from work.

They have replaced the plugs and temporarily cleaned-up the governor. The engine now runs better, but there is still lumpiness during idle and I suspect that the problem will recur.

My suspicion is that because the problem is still present when the engine is warm, it's not the warm-up governor.

Any thoughts, gentlemen? Is the governor the likely fault, or are there other faults that could be causing this? Such as the overvoltage relay or distributor? I can't afford to get into one of those ghastly situations where you end up replacing part after part in the hope of tracking down a problem ...

1977 W123 280E

[This message has been edited by AucklandGuy (edited 07-17-2000).]

[This message has been edited by AucklandGuy (edited 07-17-2000).]
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Old 07-17-2000, 05:59 PM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
After owning several of these cars, I can tell you that if everything isn't perfect they won't run well. First thing to check is the compression. Were the plugs covered with black soot or was it oily? What heat range of plugs are you using?

27 YEARS DEALER M.B. Shopforeman
1986 190E 16V
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Old 07-17-2000, 07:10 PM
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The car had compression of around 175lbs on cylinders 1-5, and 115lbs on 6. The engine was rebuilt at around 210,000km and we suspected busted piston rings on no.6 cylinder.

But then the head gasket blew, and revealed corrosion and slight warpage on the head around cylinder 6 - probably because the head was not torqued down properly after the previous owner had rebuilt it.

The head has just been resurfaced and new valve seals fitted, plus one new valve on cylinder 6. The mechanic believes that this will have solved the compression problem, although it has not been tested.

After the lumpy idle and misfires, the mechanic found that two of the new (China-made) Bosch plugs that he fitted were oiled up. He wondered if he had a bad batch and replaced them with NGKs but I don't know what the temp range is. The idle seems a bit better now but I suspect it will revert to the original lumpiness soon.

I was wondering if ignition or electrics are faulty, causing erratic plug sparking? The lumpy idle occurs no matter how warm the engine is.

Does that help?

1977 W123 280E
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Old 07-17-2000, 11:26 PM
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Join Date: Apr 2000
Location: Falls Church, VA
Posts: 5,315
My beloved 280E had a rough idle when I bought it with 97K miles. I took it in for a major service, and spent about $800 trying to fix the idle. New injectors, various valves, etc. The result was a slight improvement. It still idled lumpily. It also always cranked for a long time when starting warm - not hot or cold. No one could figure that one out.

You will probably never get the idle smooth, but it should run well. I assume you have checked for a weak spark?

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Old 08-31-2000, 06:46 PM
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The problem turned out to be the warm-up governor. It was partly corroded and not working properly, so the engine was getting flooded.

This is now fixed and the engine is purring, with 287,000km (178,000 miles) on the clock!

1977 W123 280E
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