there is NO dead end, unless you want to give up and take it to a diagnostic based shop?
Your IAC works, the wiring is good, and the ecm has control
There is NO base idle reset with a HCI change, base idle reset is for stock engine airflow
After a HCI, depending on cam, will open the throttle stop, so that idle is no longer controlled by the ecm, like a carb
people that do this dont know how the ecm controls idle speed or dont want to do it correctly, recalibration is the only way
are you running the stock throttle body?
the ecm has adaptive learning, this goes for fuel, and idle speed control, the more starts, the more driving, adaptive will start adapting to achieve target conditions in the calibration
since you cannot meet the calibration conditions, things get worse
so now that we have proven the IAC works,
its time to start at the beginning, check for codes.