https://www.ford-trucks.com/forums/1...r-testing.html

 

Have you checked for codes? I just looked back through the thread and don’t see any mention of it!

 

Tested the vacuum today with the truck idling and got 20 inHg. Shut the truck down and the vacuum held solid at just above 20. This is good vacuum, right?

 

Yeah, that’s good. Problem still happening?

 

Yeah, but I have just been using it without the IAC plugged in. It would be nice to get it working though. No codes either.

 

If you take a piece of construction paper and place it over the throttle bores, will the motor die? You checked the upper and lower intake bolts for tightness since the rebuild?

 

I will check, but how could a potential air leak cause the rpm to "stick"?

 

What you’re trying to fix is how your truck can operate at 750-800 rpm with IAC unplugged and idle stop screw all the way out. When that’s remedied, the you can plug the IAC back in to function. It needs things to operate correctly in order for it to do the same. Otherwise, the computer gets confused and signals the overrun. If a vehicle would be at 500 rpm without the IAC and 850-900 with IAC, you introduce more unregistered air and you have a high rpm. The computer sees the tps is closed or part throttle voltage and tells the IAC to open so it doesn’t fall flat. Once that happens the leak causes things to go haywire. Make sense?

 

ohhh, Now I'm wondering if the IAC-unplugged idle is set right... hmm.

 

It’s definitely not if you idle at 800 rpm unplugged. Set correctly the truck should almost die unplugged. Before you try to reset it, put your timing back to 10 degrees also.