I just got my 1990 gt running good now my only problem is that it idles high when the clutch pedal is released. (1500-2000rpms) when the clutch is engaged whether the trans is in gear or in neutral it idles perfect right around 800-1000 rpms with minimal surging. i rebuilt the motor last summer with a set of gt40 heads and intake, b303 cam and mac longtube headers. ive worked out all the bugs (i think) except for this one. and i have never heard of this problem before. any ideas?

Hard to say. Good place to start would be vacuum leaks, but I'm thinking this might be related to the neutral switch, I just need to find out what year the ECM programming included an idle bump for shifts.

im 99% sure there arent any vacuum leaks. as for the neutral switch, is that located behind the clutch pedal?

Nope, the clutch switch on the pedal is to prevent starting in gear. The neutral switch is on the trans, up near the shifter. Should be a 2 prong.

Had same problem when I did some mods. I had a clogged IAC and an exhaust leak. Not sure which exactly was the issue.

i do have an exhaust leak that i just havent gotten around to fixing, but im pretty sure i cleaned my IAC motor before putting it on.

unplugged the neutral switch on top of the tans and fixed my problem. purrs like a kitten