Hi,
Our 300E started to run a bit rough a week ago, so I decided to check it out. I pulled the plugs and one of the (#2) was oily and had some sort of collected debrie on it. It's solid and I am not sure what it is. I will post a picture of it later.
What could cause this to happend? It seems to have melted onto the plug itself - probably from the sparks themselves.
After changing the plug it ran a bit rougher too, as it's misfiring.

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99 W210 E220 cdi sedan automatic (248.000 km) 210.006