On the throttle body. Here's a pic on this link hope it helps. http://www.fordf150.net/howto/throttlebodyclean.php

 

It could be a your mass air flow censer. That's what mine did when it went bad.

 

Do u have a KandN in take. Cause there known for the oils of the filter to get on the mass air flow censer. An if that's the case u would just have to clean it.

 

Yea I have the k&n intake I will clean it I checked the iac valve and the spring still moves when you turn the key so I guess its still working

 

On the 5.4L it is on the back of the throttle body close to the firewall. 8mm bolts hold it on

 

I have the 5.4 but if it helps, mine was doing the same thing and it turned out to be a vacuum line on the very back of the intake. It had rotted and fallen off. Replaced just about every sensor on my truck before I found it. Check all your vacuum lines first. Could save you some dough.