You cannot set the base idle with the srew, the computer will continuously compensate: meaning you could back the screw off anywhere from 1 - 6 turns and the idle would be the same up until the point where the computer has the IAC all the way open and it can no longer adust, and that point it would start to idle too low and probably stall when put it in gear and turned on the A/C.
What you are adjusting is really the base airflow rate independent of the idle air circuit. Just back the screw off about a turn or so at a time until the idle behaves properly. The idle speed in gear and out of gear will be controlled by the computer. Go test drive it and keep adjusting it until it seems right.
If you have the screw opening the throttle too far, the idle will want to hang up high for too long when slowing. If you have the screw allowing the throttle to close too much, it will want to surge when you come to a stop, with the idle speed temporarily dropping too low like it wants to stall and then hunting a bit.