Well, a quick update - my idle speed, even when down, was hovering just over 1000 rpms, so I dialed the idle adjusting screw down a quarter turn to reach somewhere in the 850-900 rpm range. I also found a hose connected to the EGR valve that wasn't securely attached.

Third thing I noticed was that by pulling on the throttle cable and releasing slowing, the cable would seem to release all tension, throttle cable pulley would also, but the throttle valve wouldn't fully close. A quick pop of the throttle would resolve this issue. I wondered if I had the same issue as PETDOC with the cable sheath, but after inspecting the cable seems to be moving freely, and I don't see any signs of excessive wearing. I checked the throttle valve spring, and it has plenty of tension and closes fine when moving the throttle valve by hand. It only stuck open when it was moved by the throttle cable pulley. Seemed to be related to the linkage between the throttle cable pulley and the throttle vavle pulley. The linkage was a bit tacky at the ball-in-socket joint connecting to the throttle valve pulley, so I cleaned that up and re-greased.

After these three changes, I haven't had a significant stuck high idle yet, but it's only been a day:)

Question: Is it even possible that the throttle vavle could be stuck slightly open due to a tacky linkage between the throttle cable and throttle valve (knowing that the throttle valve spring is good), or is it soley a vacuum leak that is forcing the throttle valve to stay slightly open?