Thanks for all the input and willing to help guys!
Busy time of the year
but I managed to get in the shop last night and shot some movies to post here. In the process, I figured out the answer to my question!
Under PWM hardware settings there is a "Min PWM Duty Allowed" setting. When the limit is reached (and rpm still too high) the whole idle control algorithm stops, It's not just "clamping" the output.
I was expecting (especially since the IAC On flag was ON) that the algorithm would still work (see the numbers change) just that the output would be clamped between the min and max settings. Anyway... nothing wrong with this. Just different than what I thought.
Now we can talk about throttle body control
The problem for me seems to be that the
air intake temperature makes a BIG difference on how much the throttle body needs to be opened and the "Min PWM Duty Allowed" seems to be the MAIN thing that prevents the engine from stalling when the revs are dropping (like revving it in neutral and letting the engine settle).
This setpoint however is not scaled with temperature, so no way to tune it for both cold air and hot air.
This car runs on E85, 1700cc injectors, and liquid (ice) to air intercooler... AND it was like -10deg outside recently. Starting the car, IAC is ~0degC, then once the engine warms up and the underhood temps go up, IAC is ~65deg.
So... let's say I set the min pwm to ~20 which is perfect when running with hot air, and then I open the hood (on turn on the intercooler pump), engine gets cold air rpm's go up and no way to close the throttle body.
If I set the min PWM at 16, good for cold temps, I use the other functions to get good idle and everything works fine until I try to rev the engine and let it settle. When I do that, the PWM drops to the MIn Allowed (16) and the idle control cannot catch the engine, so it just dies.
Now I'll post the videos.