On my last trip out of town I had this intermittent situation happened three times. After stopping the car and shifting the trans into Park the engine would rev up to 2500, one time as high as 3000 RPM. I'd shut the engine off and it would restart and idle normally. It was quite hot here last week, and it has never done this before. I have to go out of town again next week, so I'll find out if it does it again, but what might cause this kind of situation?