yea, i installed bosch 4 prong plugs, and my car ran like shit, then i put some cheap brand single prong in, and it's running like usual. but the kick at 4000 seems like it could be the VRIS plates, cause they kick in at like 4250 or something, i don't know if the timing would have screwed with those or not, any way, i have oil in my plug wells too, and it's killing me, if i don't want to have the weird flat spots, i have to replace plugs every 2k miles. it's a real pain. anyway, let us know how it works out, good luck!