I'm having some troubles with my L31 vortec manifold swap. The truck runs great but it wont idle so I haven't actually driven it yet. First I had my IAC wired wrong but figured that out last night. It is all the way closed and will not move, if I remove it and push in all the way like its open then re-install it immidentally closes. Is there a test procedure or something I can do to tell for sure if its bad before I drop $90 on a new one? I always thought you sohouldnt be able to push it in or out, that only the motor could move it, is that alone a sign of it being bad? It doesnt throw a code when plugged in though.

You can jump the ALDL and cycle it. Search for which terminals to jumper. I read not to cycle while out of the TB.

It sounds like the IAC is still not wired right if it closes right away. The newer delphi IAC is a bit different than the older ones. I think the stepping logic is the same as the earlier IACs, but it could also be different.

Part of the problem could also be that you have the wrong calibration for the IAC. You will need to change your IAC steps vs. % airflow table as the delphi IAC takes ~2x more steps to open than the older IACs (0-320 vs. 0-160). The PCM will not be able to fully open the IAC as it can only register up to 255 steps, but changing the table out will make the engine idle better as teh PCM will know how far to open the IAC. I attached the new table below from my vortec PCM. IIRC, this should be defined in the XDF for the $0D.

I have a successful wiring schematic posted early this year or last. I adapted a 1995-1996 7.4L TBI to my stock harness. Search if you care to.

Thanks didn think about that. My truck still isnt running, hopefully tomorrow when I get my new fuel pump in.