I was trying to track down a drivability issue that included an idle problem and figured the solution might help some one else.
I tried a bunch of other things with no success. I decided to switch out the Idle air control solenoid with a spare one I had.
I took them both apart to make sure they both worked and where clean, and low and behold, the one I was using on the car was missing the rubber oring that keeps unmetered air from entering the IAC.
You can see the Oring on the right
Here you can see the oring on the solenoid.
I had bought a used Ford Motorsport 65mm throttlebody off eBay and either it didn't have the oring in it when I got it, Or I took it off when I was cleaning it and forgot to put it back on.
Basically a 2 cent oring was driving me nuts.
Car idles fine now.