Mine was backfiring HORRIBLY and 3 cylinders weren't getting spark. (Unplugged 3 coil packs that did not affect idle.) After wracking the brain we finally thought to pull the PTU connection apart and clean it. Some QR cleaner, a wire brush, and 5 minutes later - it was like a brand new car. Funny what a difference that little bit of corrosion made. Good luck.
If I would have known addiction was this expensive I would have seen a shrink a long time ago. --BadZCar (FL)