Do this: start the engine cold. Then, unplug the IAC pigtail. If it instantly stalls, the IAC works when cold. Now, plug it back in, restart it, let the engine get to temperature with the hood down (to hold the heat in). When it's good and hot, lift the hood, unplug the IAC. If the engine stalls, the IAC is good, and you have another problem. If it doesn't stall cold or hot, replace the IAC.