hey i recently had this problem as well but with my 97 z34, i tried replacing the plugs,wires,fuel filter and egr valve. when i was about to give up on it i went to auto zone and one of the guys there recommended this sea foam upper engine cleaner, which can be used in the vaccum lines, oil and fuel. so i took off my egr valve and dumped about a qaurter of the bottle down in there and then put my egr back on and started the car, this helped a little but the same problem was still there. so i changed my oil and added the same stuff to my oil(what was left in the bottle). and when i took it out on the road i instantly felt the power come back and the boging stopped. turns out there was alot of carbon build up around my lifters which caused them to stick bad. i know they are 2 diff engines but this is deffinitly something i would reccomend befor blowing all your money on parts that just wont do anything. the bottle runs like $10 at autozone and i use it during every oil change.