joshua perera

W207 2011 e250 cabriolet. On idle it shivers. Why has the spark turned black and white. It’s only 8 months old. Previously there was oil in two plugs which I cleaned. Also one coil misfired. Fixed all these. Could this be the cause or is there something more to this ? Today I replaced all four sparks shiver has gone away from now. Any help ?

WRC-LVR

When you changed the plugs, did you put a little bit of dielectric grease on the ceramic body of the plug ( above the steel body ) on the "ribs" If not i suspect the spark is jumping down the body of the plug rather than staying internally and firing to ground at the tip as intended,,,
If I was you i would check the plugs that were removed to see if you see any slight tracking down the ceramic body to the steel body. If so then you will need to inspect the coils for acring inside the boots.
You said you replaced one coil...the others may need replacing too, if they are arcing to ground internally in the boots. When you replace them put a little bit of dielectric grease on the boots inside to ease in future removal. Whatever you do DONT get the grease on the metal conductor inside the coil boot NOR on the end of the plug that connects to the coil inside the boot.

Chevota

Looks like a classic rich fuel mix to me. I'd suspect the O2 sensor. If the O2 is old I'd swap it out and see what happens. I wouldn't say there is a time threshold for "old", more like miles and how much crap they get coated with. Many of them need access to ambient air, as a reference, and if that's blocked by crud it may force the eng to run richer. The first O2 in the system is the one that dictates fuel mix, and I'd assume easy to get to in yours?

WRC, why the concern about dielectric on the contacts? I always coat those well to limit corrosion, after having some basically dissolve when I was a kid. The trons burn right through whatever thin film exists between the contact points.
I don't put any on the plug, but I put a lot in the boot. When I pulled off my oem coils/boots, after being on there for ~7, years I was wondering if they mistakenly used epoxy. Removing those boots was the most difficult part of the plug swap.
The new boots on the new coil assy had some grease on them but not what I'd consider enough. And it looked like grease, not silicone. I removed that stuff and douched 'em with silicone. O-ring lube to be exact