Apparently IAC's aren't necessary. I went to put on my polished/half-shafted TB and forgot to reconnect the IAC. I was still able to adjust idle, but it would dip bad when it was put in gear and I didn't know why. I didn't get a CEL which was kinda wierd, but I thought I'd share cause someone had an idle problem a long time ago and the idle was still too high after disconnecting the IAC then it turned out to be a bad IAC. Hmm.....