These are not sophisticated enough to have automatic idle control. Try adjusting the throttle stop screw, not the synch screw. The throttle stop is above and behind the synch screw which is on the right side throttle shaft. The throttles may also need to be synchronized but try the stop screw first.
There are three adjustments on the throttle linkage. The idle adjustment screw is in the middle of the throttle linkage where the left and right throttle linkages join, middle at the rear of the engine. the cylinder bank sync screw is behind the CFI cover on the right side of the engine - if you adjust this screw without having vacuum gauges connected you will throw the cylinder bank balance out, and will have to use vacuum gauges to bring the cylinder banks back into balance. The third adjustment is behind the left CFI cover. It is a small screw that when the engine TPS is calibrated, it is to be backed off and tightened with a locking nut so that the throttle linkage is not impacted.
I have my air chamber out because I had to fix the air filter box securing arrangement and I replaced some IAC and vacuum hoses.
The first picture is of the idle adjustment screw in the middle of the throttle linkages. You can see how the throttle linkages are connected and the idle adjustment screw. The screw pushes against a stationary, non adjustable stop.
The second picture of the cylinder balance screw that you find behind the right side CFI cover, on the right side of the air chamber, shows the cylinder balance screw pushing against the right side throttle linkage. Behind the throttle linkage is a spring pushing against the throttle linkage opposing the force of the screw. There is no other adjustment. This screw is only adjusted when you do a cylinder balance.
The third picture is of the TPS calibrating screw. When not calibrating the TPS the screw is as I mentioned backed off and locked in place with a lock nut. You can see the space between the screw and throttle linkage.
The fourth picture is off the throttle linkage as attached.
Another item to check is the throttle cables. I was having trouble getting the throttle to return to idle without having to manually assist. What was happening was the cable had cut into the internal sheathing and was binding - after 32 years can be expected.
Check cable adjustment and routing as well. The routing of the throttle cables can cause the engine idle to increase if it is not routed properly.
For the IAC system, this is my thread on the Classic forum with pictures of the IAC internals. Replaced the IAC valve for a different reason, didn't fix it but I now have a new IAC valve installed. Here is the thread: https://www.classicgoldwings.com/for...+valve#p206808
Hope this helps. Cheers