hi all,
i have r34gtt had the same popping misfire after 4000. I checked my coils because that seemed most likely. However, they were brand new the car has only done 55000km. My problem only started when i changed my plugs over from standard to iridium. so I tried gapping them to .75 that didn't work then i gapped them to .6 that seemed to fix the problem but i still get the mis every now and then most of the time it works no miss. So i guess its the plugs so for those of you that are thinking about changing plugs don't get iridium they seem to be my problem. i will get some ngk copper plugs and change them next possible chance i get i will keep you all posted and let you know if it worked.
any other suggestions advice would also be good.