Engine won't idle down.
So its either the TB blade sticking partially open when you release the "air" pedal. Or your IAC (idle air control) valve is sticking partially open at times.
----It could also be a vacuum leak, allowing more air into the intake. But you said it corrected itself when you got home. I would think a vacuum leak would remain a leak until its fixed. But you never know.
So pop off the air bellow/hose and clean all inside the TB housing and the blade itself. Use Sea Foam spray. Then take the IAC valve out and spray it real good.
Take the IAC valve out really slow so the little spring doesn't go flying......
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