HI,

Well a half turn is way too much!
I would have the screw do exactly as you described to just touch the lever.
Then I like only giving it another little twist about the width of the screws slot for the screwdriver.

All you want to do with that screw is to provide a resting spot to hold the plates outer perimeter surface from being hammered shut into the walls of the bore by the return springs pressure.
We want the plate to close in such a way that it's up and touching without pressure to tightly close it so it cannot get jammed or deformed from a sudden rapid release from a wide open position.

The cable pulley above operates without any stops even though there are tabs on the pulley they are not used. They were used and there for earlier micro switches on K jet systems and alike come up in design of the 240s.
They got replaced by the Bosch shaft switch TPS and LH system.
So you want to make sure that the cable itself has some slack going over the pulley drum too.
This allows for the engine to rock and shift on its rubber mounts.

Don't get to wound up worrying about the linkage rod in between.
As you will see ,its adjustable, but its set purpose is to keep the throttle pulley tabs away from their stops above so all can get to close the throttle with the return spring that's pulling the foot feed cable.
There might be a specification for the tab space distance, someplace in old manuals, but it really is, "Don't have it touch!"

Bottom line the plate is too be or get closed just as important as they now do inside the IAC!
The older IAC's were held closed electronically and this presented a "minor" safety issue that was addressed after around 1987-8, I think?
The throat size of these IACs, are or were, intended to be self limiting by design, so, that's why I say "Minor."

Still a "high idle" is a little unnerving in any case!
All the LH systems use the ignition system RPMs and a computer program to set the idle speed of 750 rpm.
The days of a higher idle speed due to air conditioning loads are instantly adjusted by these IACs.
In the early years of say around 1983-4 LH 1.0's we saw all the electrically controlled vacuum "leak" valves, disappear!
Mainly because that leak was behind the AMMs and raised havoc!
I imagine that Emissions was the motivation between several groups of design desks!
A push for Lower "idle emissions" was the total goal, so no more 1000 RPMS for the A/C load allowed.
Shortly there after, we got ridiculous, with heated Oxygen sensors to speed up process, when lab technicians got more persnickety! (:)

Yep, back up the screw a little bit!

Phil