Try spraying some carburetor cleaner around the intake and push the plate down and spray some inside there too. It sounds like your air flow plate is sticking, or it could also be the air flow position sensor -- but I'd put money on the former.
If you're seeing temp needle "bounce", check the single pole temp sensor just forward (on head) of the two pole ACC temp sensor. If connection is good, try a part swap out and see what happens, if you haven't already.
G'luck
