How does the auxillary air slide close ?
Does it ROTATE closed as the spring heats up or does the spring PUSH or PULL the piston slide closed? Doesn't look like there is much room for vertical movement looking into the port.

My engine idles about 200-300 rpms too high and I know the valve is not closing as there is air that passes thru the valve when it has reached operating temperature when I test it. There are no other vacuum leaks.

I've PB blasted the valve several times. I wonder if the spring is broken or internal screw that locks the spring has failed.

It rotates. The spring is bimetalic. As it heats up the "piston" rotates and the slot in the piston closes. The spring is heated by both engine heat and heat from 12 volts.

When attempting to restore an old not fully closing AAR, first determine that it's heating element is working by connecting to power source. Soaking in PB Blaster usually works, but sometimes needs a few times to work. On the ones that are still resistant to fully closing I use this method:

Cool the AAR till it opens enough to insert a pick, very small screw driver, or the like. Attach the power to make the valve close against the "pick". At that time use the pick to open the valve as much as possible and then quickly remove the pick to allow the valve to "slam shut" Spray again with PB and repeat. This action, by breaking up any residual obstructions to the valve's closing, will allow the valve to completely close on it's own under normal operating conditions. Contrary to popular belief, almost closed is not acceptable for the AAR, It must not allow any air to pass when closed.