Idle issue. Any ideas?
 

I have a 91 gt all stock. When I start the car I have about 3min of good idle. After this I get a very lugging idle if that makes since. It seems to idle from maybe 800-850 rpm then drop to maybe 650-700 rpm then back again. As soon as I hit the gas it clears up and runs very smooth and strong. The only real issue I have with this idle is it makes it hard to idle through parking lots without jerking your teeth out lol. Any ideas to clear this up would be helpful.

Remove the IAC and clean it and see if that helps.