I switched my IAC with my friends "healthy" cobra and his ran the same, thus eliminating the possibility of my part being "bad" As a matter of fact, we didn't even switch them back - I just installed his on mine and we agreed and classified it as "Man Law"...I would start there if you aren't sure the IAC is the problem - try and find a buddy that will use his car as a donor(takes 5 mins) and check yours on his or vice versa.
My idle problems were corrected when I tightened the screw that controls your idle - I lowered it effectively and my car began to idle at 900 rpms instead of 1100 and stopped throwing codes that traditionally were associated with the IAC.
Moral of the story, try and locate your problem, eliminate as many culprits along the way. In my case, I ruled out the IAC and saved myself a $100 b/c I would have ordered the original from Ford only to have my engine still throw codes.
The idle screw can be manipulated if you have done any work underneath your hook so I would check that to see if it is your problem...
