Girlfriend drives an 02 F150 with the 4.6L. It ran like a top until recently it started to idle very high at a warm start (2000rpm) for about 20 seconds before dropping to normal. Eventually it started to surge up and down from idle to 2000rpm and became difficult to drive. It was almost like having a stuck throttle. Finally it would rev up and down and stall out.

My first thought was to replace the Idle Air Control valve. This worked wonders and the truck would at least run again. It still idles high (1500rpm) but will eventually drop to idle and still pulls while coasting in gear, if I drop into neutral it will eventually drop to idle.

I hooked a diagnostic tool to it and looked at the throttle position sensor readings and they are normal and consistent weather or not it is idling normally or high. I sprayed with starting fluid (engine cold) to look for vacuum leaks and found none.

I will also add that at no point has it thrown a code.

Any ideas?

 

Mine did that the other day and even though my tps read normal I had an extra so I swapped it on and viola! It still runs like a charm.

 

The gremlins the plagued my truck seemingly overnight was a few things. All of them slightly helped the problem until it finally went away.

Changed the TPS, not much change.
Replaced vacuum line from the back of the intake, slight change. (It was nasty greasy and there was a hole in it.)
Replaced PCV, Most change so far
Charge my HVAC, Final minor Change and the high/erratic idle is gone.