Ok, here's an interesting one. I adjusted the mimimum air on my 91 GTA yesterday. I put her into diagnostic mode and waited about 45 seconds, then I disconnected the IAC as per procedure. I then went ahead and started the car with the IAC disconnected, but she would fire then die immediately, so I cracked the throttle blades open a little bit until she started and I did the adjustment. Shut down the car, reconnected the IAC and started it again and the idle was smooth as silk at my commanded RPM of 800. (I'm tuning a chip for the car, transmission is T56 so it is not in drive). I shut down the car and turned it back on again and the idle was at 1500rpm.

I put the car into diagnostic mode and disconnected the IAC again (after waiting 30 seconds) to re-do the minimum air adjustment and it's almost like the IAC did not move at all. I started the car and the idle shot up to 1500rpm. So I shut it down, reconnected the IAC and this time, while key on, I waited 2 minutes before starting the car and the idle was low again. Readjusted miminum air, shut down, reconnected IAC, started the car again, idled smooth again. Shut down, restarted and it was back at 1500rpm. Anybody every run into this problem? Any suggestions?

 

I had alot of minimum idle problems when my injectors and regulator diaphragm were leaking. The mixture was too rich to even run at minimum idle. Do you have the original injectors in there still? What about the regulator diaphragm?

Sounds like the procedure is correct...I can't imagine what else.

Hope this helps.

 

No, the injectors are Ford 39lb and the diaphragm is new since it came with the Accel adjustable fuel pressure regulator. The tune is a little rich, but before I actually start tuning it, I want to get a decent idle. What gets me is that whenever I do the adjustment, the car will idle excellent the first start-up after I do the adjustment, and after I shut it down and go to start it again, the car will idle at 1500rpm.

I did check the IAC readings with a scantool. After the minimum air was done and the car was started with the IAC connected, the IAC steps would be in the 25-30 range. After I shut down and let the car sit for a few minutes, the car would idle at 1500 with the IAC in the vicinity of 120 steps.