My 32 gtr starts and runs excellent when its cold, but as soon as it get's hot say maybe 10mins into driving it feels like it drops a cylinder and runs rough as hell. It blows black smoke when it does this, and continues for about 10mins then clears up, then goes back to the same thing. Ive changed the plugs and the coil packs, was thinking it could possibly be the igniter. Has anyone come accross this problem before?