2000 f150 4.6 auto
when I start the truck, the engine idles real high. If I unplug the iac, the idle drops right down. I replaced the idle air control a few years ago. The only way to drive the truck is with the iac unplugged. No engine codes till I unplugged the control.
Could it be the throttle position sensor? what should I check?

 

Why wouldn't you suspect the IAC again? You said it yourself, the idle changes when you unplug it.

Could be stuck open.

 

Are you sure you have an F150 there? Explorers and Mountaineers came with the 4.0's.

Nevermind, you edited that. Makes sense now.

 

I removed the iac, and it's nice and clean. How bout the tps?

 

I have an old Jeep too! It has the 4.0, used to writting about it.

 

Replace your IAC.

 

Ahh, that explains it lol.

 

Is that the gen. consensus? Replace the IAC again?

 

The IAC is directly related to voltage applied, from open to shut. Supplying 12V wont tell you much.

Check out this page, - scroll half way down to IAC, -

http://www.fordscorpio.co.uk/ccmonitor.htm

 

"The IAC is checked electrically for open and shorts"
So, unplugging it, and the idle drops, plugging it back in, the idle races. Does that mean anything?