had a similar prob with my car found that the plugs had been changed to standard type,(not platnuim)and because of the larger electrode size more voltage was need to create a spark, so the coils had been arking between the top of the plug and the coil creating a miss fire. Also the under bonnet temp roots the coils and that stupid cover on top of the coils has to go, more heat, more resistance, less spark!
to beat the leaning out prob i brought a after market fuel presure regulator cranked the pressure up to 45psi
hope that can help u out a bit, but a question for u? have u had the speed cut removed if so witch wire do i chop, Also tryin to find out if my car has a "speed signal wire" so i can hook up a Greddy full auto timer, finding it hard to get hold of a wiring diagram. My car is a 1990 R32 GTS-T type M :headspin: