To tie 1TMF's and Grady's posts together (I know what you both are saying): Do the test on a colder motor (where the IAC is needed as part of the enrichment function). As Grady said, some folks (like me) have the hot, no-load idle set for zero DC from the IAC (so the test is invalid on a hot motor).
To test the IAC in its true dynamic, you can hook up an oscilliscope and check out the square wave - that's above what most of us want to do.
Good luck.