2003 F150 4x4, V8 motor, RPM's occasionally go to about 1500 when put in park or neutral. I can feel it when in drive as the truck takes off pretty good when break is released. If I shut the thing off and then restart it the rpm's are normal. No check engine light, no nothing. When this happens it is usually after a short drive. Thanks for any help.

 

Ttt.

 

Maybe the IAC sticking? Easy to remove and clean to rule it out anyway.

 

Check for vacuum leaks. The pcv vacuum circuit that have the 90 degree elbows in them are the ones that get leaks and are sporatic and make the idle act up.
Replaced mine and it stopped the problems that sound a lot like yours.