Ok where do i start i swaped a car for a gts-t m-spec skyline its got a standard rb20det in it. i drove the car for all of about seven hours then it started to miss real bad every time i hit boost. so i suspected coils and/or ignition module i replaced both but no change. so i pulled out the plugs to find each one had melted the tips off. i brought new set of plugs it ran fine when i replaced them. Then i stupidly put regular 91 octane fuel in it not relising (half asleep) relised what i had done after filling the tank so i took it for a drive to see if it would effect it badly or not. IT DID it droped a cyl half way down the road. i took it to a mechanic who discoverd it had burned a pretty hole through the no.6 exaust valve so i had the valve replaced and iv just got it back but it still has a miss in the 3-5 rev range then it smooths out ive had the injectors and coils tested and they are mint. i still have no idea what it could be any help would be great cheers.