What controls the IAC.

I have a problem with my 5.0 that idles to high. NO vacumn or Air leaks. I changed TPS MAP and IAC and Computer. Still can't get the idle down. I cut open the harness tape to look for shorts nadda that i can see.

The signal volatge is 5v to TPS, egr sensor and MAP.

I read a constant 12v on the IAC. If I disconnect the IAC wires then the truck idles. Connnected the valve opens idles goes way up high and doesnt kick down. What else controls the IAC. I took the wire out of the harness socket and tested the voltage from there and still came back with 12v no change.

It is probably obvious but???? Could the Coolant temp sensor(changed 20k ago)or Power Steering sensor be the issue. Truck has 5.0 and 104k, manual trans 4x4.

Im drowning in wires...

 

Hi, I'm experiencing the same problem today with my E150. I have performed many of the same steps / actions as you have. I have just today joined this forum in search of an answer to this problem my van has.
By the date of your post, I realize it has been some time since you posted this, but I am wondering and hoping you discovered a solution and would share it with me please?
I would greatly appreciate this!
Thank you.