280SE - missing cylinder - lumpy idle

My 1984 280SE (Euro) 240k km., was misfiring occasionally at higher revs. Blue sparks on the distributor cap, (corroded coil terminal, probably the original cap!) 2 (!) plug electrodes almost eaten away, so changed all HT
leads, distributor cap, rotor arm, oh and new plugs ! Now pulls strongly from 2000 to over 6000 rpm, but idles like a 5-cylinder. No oil in the water, no water in the oil, spraying diesel start around can't find any intake leaks. Are we talking head gasket between cylinders, or leaking hoses or what ? Any help appreciated. David Westerman
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First isolate which cylinder misses- unplug the sparkplug leads one at a time and see which cylinder does not drop off. Then check that cylinder's sparkplug (or just change it); check for vacuum ports at that location on the intake manifold; and do a compression checkif nothing else appears likely.
Bill Ditmire Ditmire Motorworks,Inc. 425 White Horse Pike Absecon,NJ 08201 http://www.ditmire.com 609-641-3392
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Improperly adjusted distributor points can cause a rough idle. You put in a new set of points, right?

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Possibly a bad spark plug. Yes, new spark plugs can act this way, it just happened to me with some Champions. Spark plugs can be tested, or, buy one more and install it in #1, if that doesn't fix it install old #1 into #2 and so on until the bad plug is revealed.
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I was unlucky enough to have 2 bad brand new plugs plugs. It happens.
If you do a compression test and it all looks fine, its a plug (or two). Just try another 'new' plug.
........ Rob.

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