Actually, problem solved. Like I said, we had changed everything else I could think of before this problem even started, so I was afraid of this. I wanted it to be a last resort, though. The computer was apparently bad. I figured something was up with it, because there's no way 3 IACs were bad, yet when I unplugged the IAC, it started up and idled by itself. So there you have it, folks. She's back to purring like a kitten.