With the stop screw backed out, is the throttle lever all the way back to the ear on the throttle body? I mean the return spring ain't worn out, is it?
The next step would be to check the throttle position sensor.
Is there any way of taking the IAC off the car and somehow plugging the holes with a shop rag or something similar? (something that won't get sucked into the motor) The reason I ask is I think if you can do that the air that would normally enter the engine with the IAC in place will no longer get in there. So if the engine still revs to 2K then you know the problem is elsewhere. However if the engine rpms drop when those holes are completely blocked then your problem may be with the IAC or the wiring to the IAC. If that's the case then you may want to try swapping another IAC in there. I know it's new but I have known people who've gotten rejects from time to time. If that doesn't work then try looking for shorts or open circuits in the IAC wiring.