Has to be a leak. No way around it. Check and see if something is holding your throttle body open, and then start looking for gasket leaks, caps missing off nipples, lines broken..its a big leak and you should be able to find it. Spray starter fluid around all the sealing surfaces and listen for idle changes.

The iacv cracked wide open couldn't make your car go to 5k, and right now its gotta be closed all the way trying to bring the idle down. Stick your fingers in the ports in the bore of the throttle body and see if it drops.