Latest update.

I tried a different OVP just for fun and no change. I removed and reinstalled several vacuum hoses and sprayed a little silicone on the throttle linkage and now it "intermittently" settles at 500 RPM.

So I must have done something to the system, but I'm still stumped as to why it has improved.

My worry is that it still sticks at 900+ RPM occasionally.