Ok, I haven't posted in a while but this one is driving me crazy... NA1.8 ...
Every ~3 weekends, I look at my plugs and it's now the 3rd time I find this. Always on Cylinder #3:
And best of all, the engine is not running rough... Maybe a little down on power but no significant changes.
I looked with a bore scope and the piston/chamber looks fine/identical to the others.
I tried Autolite as well as NGK, same result.