Ok this ? is for my 88 GXL auto. (daily driver) It has a relatively fresh engine (under 20k), with Bonez race system and N1 exhaust (don't ask).

It runs and idles fine if you just granny it around but if you redline it the idle gets messed up and goes from 500 (almost stalling) up to 1200... up and down, up and down. If you slam the brakes or shift into reverse it will stall completely. The only way to "fix" the idle is to turn on the A/C then it goes to a rock solid 1000 rpm idle.

When I installed the bonez pipe the 6 ports were working, but they could be stuck now (I haven't checked them).

 

Check the BAC, it is your most likely culprit.
hanman