I had a similar experience happen to me on my X. It was in Jan 05. It had about a 1000 miles on it and I went to start it one morning (it was cold but not freezing) and the idles seemed normal but then I started to hear the car rev ( it went to about 2500 rpm) by itself. It was in park and I wasnt even touching the accelerator or the brakes. I turned the car off and started it again and the temperature needle went all the way to hot. I shut it down and the started it again, everything was back to normal. I havent had that happen since. I guess it was some sort of a glitch.