moving the TPS voltage has no affect, it zeros RATCH.
TB position, is airflow dependent, you need to tell the ECM how much it flows at closed throttle, that is how idle speed and IAC function in concert.
You are not going to change the duty cycle, you are going to change the amount of air, the IAC transfer will dictate, the duty cycle, you do not want to touch the IAC transfer.
air entering past MAf=to TB air + IAC air.
750 rpm idle=a certain amount of air in the Maf transfer.
you want 750 rpm at some idle state
that maf voltage = air=TB air,,,,,,,then the IAC adds or takes air away so the MAF = 750 rpm air/voltage measured.
So you see its key to have the actual TB air to be accurate.
Ie within the ISCKAM limits.
89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.