my ITA 89 240 Sx is experiencing some form of intermitant ignition problems - above 3000 rpm the tach bounces wildly sometimes over the rev limit. At the same time the iginition appears to be cutting out and the motor backfires - as a consequence we can't make power. This caused us to pull from the grid at NHIS this weekend. We pulled and changed the distributor, cap, rotor and igintion coil to no avail. ANY SUGGESTIONS WHAT NEXT? HELP