I've for a weird problem and I've been though a few ECUs.
16197427 5.7L on a IH 345 tuned timing and fuel to be "ok"

It always wants to idle high. So I set the idle vs temp points to all be 650. It still likes to idle at 1100-1400. Sometimes it will idle correctly. But if I start it, stop it, and start it again I am guaranteed it will idle high.

That's when I noticed it said 11% throttle on the TunrerPro dash. But the voltage was correct (+/-0.2 @.54v)

I've also had idle oscillations.

I've had nothing but trouble with my IAC. I can't get it to close on the IAC reset procedure. But it does work. I've been through multiple IACs and multiple 16197427 PCMs

I'm thinking maybe that the IAC is staying too open and isn't resetting between the engine off/on time. How much time does it need?

 

if your throttle is anything other than 0% or maybe .39% at idle, you'll have idle speed issues.

i've had an issue where if my ECM went into limp-home mode due to a bad tune(or bad contact), when i would replace the chip, TPS% was always at ~2.x% when i was at idle, with correct TPS voltage.

pull the battery power to the ECM for a few seconds, key-on, then the % is fixed.