I've got a missfire at the moment (at least that's what i think it is) consistently between 3500 and 4000rpm. I've cleaned the AFM and coil packs, checked the resistance of the coil packs, put new spark plugs in, but still prevails. Hopefully its just because i'm running rich (i constantly get backfires on gear changes and releasing throttle) and it can be sorted out on the dyno. The only thing i've noticed about the coil packs is that 5 are rb20 coils with the metal spring on the end and 1 is a later model coil pack with the black filament, could that be the cause?