I had a nasty miss, not so much in hot weather but really bad missfiring especially at night, anything over 8psi and anything over 4000rpm. RB20DET, intercooler, 12psi, R33 turbo. I finally got around to changing the spark plugs and found that the "Iri-top8" plugs that were in the car looked like they had done 2,000,000km, the electrode had been eaten away to the point that they were almost 1.1mmgap, rather than 0.8mm..... so much for the guy saying my car had been serviced recently. The coils I looked at, none seemed to have a hairline crack, but all 6 of them had fairly major discolouration due to arcing.... problem found.
Solution, new NGK copper plugs @ 0.8mm, NO tapeing/glueing/insulating of the coils, just put them back in with the new plugs and walaaaaah! the miss has completely gone (for now, hopefully forever). Ohhh and a tip for all, always use anti-seize stuff on the spark plugs because my plugs were almost welded to the head.
I figure that the first problem was the iridium plugs, maybe needing more energy to spark and secondly the plugs were waaaay worn to the point the were approx 1.0-1.1mm gap, making it even harder to spark. Hence the easiest route for spark was not to arc across the plug, but rather arc to the head, causing the discolouration/melting of the coil. With proper new copper 0.8mm gap plugs the car drives so much better.... now i just need to put it on the dyno and see what the AFR's are doing.
Fixxxer