Two months ago I changed out the plugs for the first time on this car, a 2000 C280 with 60m. The car had developed a slightly rough idle and I found that 2 of the plugs off of the same coil were fouled. After new plugs, the car ran fine but now it has that same slight roughness at idle again. I haven't pulled the plugs to see if the same ones are fouled again as I suspect but does this sound like either worn spark plug wires or a failing coil problem? Or something more serious like a compression problem in these cylinders?

Thanks,

glenmore
2000 C280
1991 300CE
1990 LS400

Hey, check it out - your 666th post!

Anyway, what was the nature of the fouling on the 2 plugs? Oily?

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666! Ack! Bad omen!

The two plugs had oily sticky varnish residue. The rest were nearly perfect after 8 years.

Thanks,

glenmore

I'd be more inclined to think yours is an oil control problem, and not an ignition problem. Perhaps valves, guides, or seals (who knows - maybe even rings?!). But I'm not all that familiar with the idiosyncracies of the V6 in your car, so maybe some of the experts here can speak up. If I'm not mistaken, I believe that V6 did tend to have oil control issues with the rings.

__________________
08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280