I have a gsr block, b16 head crower springs and reteainer, type r pistons and crower cams, camshafts, msd extewrnal coil, p28 and when my car is idling my muffler is popping like if it misfires. also when I am driving steady. it help when i changed the spark plugs and wires because the old spark plugs were new but were not gapped before being installed. and the were really black. when i changed them it helped the motor do you have any idea what it could be???