Hi,

The idle should be dead on the 750 rpm no matter if the air conditioning is on with cars that use an IAC.
That is supposed to be the beauty of the IAC with an electrical actuation.

You are either open too far on the throttle plate or butterfly plate, if it could bend in the middle. 🤫
A hinge mimics a butterflies body.😊
I have seen that type of air limiter where one side is spring loaded to close softly into the bores on carburetors or for choke variations to match closer to air density characteristics affected by temperatures. Thicker colder air requires more spacing.

The stop screw is used here for a static setting.
I’m pretty sure if you see very much light or any it is probably too far open.
Air is thin and light and can go around things 🤭 including over dams.
With that thought, there needs to be a tighter fit up within the bore.

The whole idea is to reduce air flow BELOW the upper limit of the IAC’s operating range so it does the higher idle function.
Today it’s reversed.
You set the air screw for a closed position so it doesn’t allow the cable pulley operating spring to apply excessive pressure.

On the older 240s there was a black adjustment screw.
It was used to set the lowest end of air bypass with the stop screw.
A wire was grounded to stop the IAC from opening completely in one direction.
Those earlier IACs had three pins for moving the valve each way of plus or minus.

The later models use only two pins to open the IAC against an automatic spring loaded return.
This became necessary for control simplicity and for ALL the fail safe reasonings you can muster up!

Phil