Mystic:
Techron hasn't in my Volvos the few times I've used it. I'm using conventional plugs, not platinums, which someone told me were more prone to deposits and fouling; not sure why or if that's even true. Years ago I used some "Gumout" which definitely did foul plugs. Can't speak for the other brands, as I haven't tried them. Intuitively, you would think there would be at least some impact, however.
