Did you ever find out what was causing the problem, mine does it also, especially after running the AC before shutdown. On the next start it will rev up and almost or sometimes die.

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2002 X5 4.6is
1999 C5 Corvette
1992 Mitsubishi 3000GT VR-4
1994 Kawasaki ZX-9R
2005 Mazda 6 Wagon (Wife's)
1991 Mitsubishi 3000GT VR-4