Code 33 but MAF ok

[Bandit1200]

I'm having a somewhat intermittent issue with my 1989 Corvette where the engine cuts back to idle when the car is in gear and the throttle is pressed to approximately 20%. If held there the SES light will come on after about 5-6 seconds and a code 33 (high voltage MAF) will be stored. The problem is worse on the highway and it will often "cut back" when the throttle is just off idle. If I let off the throttle the engine comes back to life again and will run normally. If I push the throttle from idle past the 30% mark (approximately) then the car accellerates fine and runs very well. If the engine "cuts back" and I push the throttle further the car will spit and sputter and will run very poorly with no performance until I lift my foot and then the car will come back to normal. It's as if the computer is reading the high voltage at the MAF below 25% throttle and below 2200 RPMs like it should, however changing out the MAF isn't working. Changing out the the MAF supply and burn off relays made no difference either. I've checked all the wires from the MAF to the ECM for continuity and shook them around during the test and no problems there. I've also switched out the TPS and it made no difference. Has anyone had this issue before? Any ideas? Thanks, Andrew