2001 Tacoma IAC triggered high idle

Hello all,
I have a 2001 Tacoma 4 cyl that runs great, except for...
When the engine warms up, the idle will suddenly jump to about 2000rpm and stay there. At this point, if I turn off the motor, it will not restart until it cools off a bit (10 or 15 min). It just cranks. Once restarted, it runs normal until it heats up again, then repeat. It has been happening for several months.

I have determined that something is triggering the IAC to the higher idle, but I don't know what.
While the engine is idling high, I can unplug the IAC and it instantly returns to normal idle. Plug it back in, and the idle jumps back up, so something is sending a signal to it.
No engine light, new fuel pump and fuel pressure regulator.

Any ideas? Thanks! ~E