I searched around here yesterday to see if I could find anything similar. I just bought a 02 LS w/ ecotech for a DD it runs fine but after driving on the expressway for 40 minutes or so at 70 mph it will start to idle weird when I stop at lights and stuff. It fluctuates between 600 and 3-400 but hasn't stalled yet. It only does this after driving for a while and then stopping. I just changed the plugs and coil pack this past Sunday. Any suggestions? I read on here that it could be a vacuum leak or IAT but my car doesn't do this all of the time.

maybe you should try searching for "ECOTEC"