Actually, you are right. For some reason I thought the TPS also had a little motor in it that could control (to a small degree) how open or closed the butterfly plate is during idle. It is simply a sensor that just sends a voltage signal to show how open it is, so my theory makes no sense. My mistake

Since the car seems to idle differently after warm up is complete when the IAC plunger is theoretically closed, and it wont go over 4K RPM's, then I would recommend he start by investigating the idle stop screw, MAP sensor, and throttle cable.

Would you say those are better places to check out first Dave?