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Old 11-24-2007, 07:50 AM
pmckechnie pmckechnie is offline
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Join Date: Jan 2003
Location: Matthews, NC
Posts: 1,356
I am just going to relate the times I have had this problem with my 500SEL.
1. Found someone (Maybe me) used a coil wire that had resistance in it.
Probably just something lying around.
2. Found a oil fouled plug. Not completely, just some.
3. Used Bosch plat plugs with resistance. Did this on a bet that it would
cause a missfire at idle. I won the bet.

I have replaced the coil wire with a new correct one. Replaced the valve guide seals.
Installed NGK BP5ES non-resistor plugs. Now I have to keep checking the tach when at a light to make sure the engine is still running.

The above things didn't come all at once but one at a time over the last 5 years. I know vacumn leaks can also cause this problem but seems you have ruled out that. Just make sure you are using NON-resistor copper core plugs, Solid core wires with the MB resistor ends called for, and you should be able to get rid of this problem. Good luck.
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