I to have the same problem with my 99' 5.9L. My Idel sticks at about 1300. havent been able to find the cause yet.... So im listening...ha

 

i've come to the conclusion that its either the TPS or the IAC or MAP sensor. Anyone have more input?

 

So, i took the IAC out and looked at it, and it had some gunk on the end of it. I couldn't tell what it was, so i cleaned it off and i was reading the FSM and it basically said its like a valve to let air through the TB so i was trying to push it up and down. It pushed up and down but not far. How far is it suppose to move just by pushing it? After cleaning it i went for a ride and about 10 minutes or so into driving it idled down to where it should be. I stopped and got something to eat and when i came out the engine was cold and would not start without giving it some gas. So the high idle is gone for now but now back to the original issue of not being able to start when the engine is cold/idle when the engine is cold.