I had a 1995 Saleen s351 that the idle would intermittently go up to as much as 2500rpm,it drove me nuts!I called Saleen and they said that it was a common problem.I ended up getting a new computer after purchasing all of the parts that you mentioned and them some.At least your car is under warranty and the dealer has to fix it.I have never had any problems with the idle on my Bullitt or any other 4.6-hope that you find it quickly without too much hassle.I think the IACm was the correct call to start.Have a great day.