my 91 f150 (5.0)wants to idle around 1200rpm and doesnt want to come back down to idle after accelerating to shift (it takes about 2 to 3 sec)I replaced the throttle position sensor and this did not help. any suggestions? thanks

 

First you will want to push on the lever at the throttle body to verify the linkage/cable isn't in a bind.Secondly,you may have a vacuum leak.verify all vacuum lines and re-tighten the intake manifold{s}.I have also noticed that a faulty CTS{coolant temp sensor,not sender}will make an engine idle fast even after a sufficient warm-up,if the thermostat is at least a 180~.Lastly,swab the throttle bores blean with a nylon barrel brush dipped in solvent while holding the flap{s} wide open.No need to get deep in there,just in the area that the flap{s} are.Good luck.
Phillip