Observations:

After installing the spring recommended above, I found that my "popping" from my exhaust during deceleration has stopped. My high idle has also lessened, but not fully stopped. ( I needed to blip the throttle once.) I infer that this was probably due to the slightly open throttle blades, allowing air and subsequent fuel to burn through the exhaust.

Also, since I assume that there is wear between the shaft and hole mounts on the return spring actuator and the throttle cable actuator, I think it may have been caused by high RPM decelerations where vacuum is tremendous (3rd gear 60+ MPH decels) and it is bearing down on the throttle blades, causing them to exert negative pressure against the spring that is trying to close them. (hope that makes sense). My boost/vacuum gauge will show 22"/hg during decel. Could that cause a stress on the throttle blades against the forces (shaft/mount) trying to seal the ports over time?