About every 3 times my daughter drives her 97 GT she says it idles at around 2500 RPMs. I saw it doing it today myself and checked the throttle plate was returning to the stop and it was. I changed the IAC with a know good one off my son's 98 GT a few weeks ago. Also swapped the TPS & MAF sensors. I had put a new upper intake on the 97 last winter so I am not thinking that it could have an upper intake vacuum leak. Any common items I can check or ways to test for vacuum leaks?