High Idle on a 5.8L Windsor
 

I got a 1997 F-250 with a 5.8L . Did a quick EEC-IV test and it came up with tp sensor was bad. Motor ran in the fault safe position, shifted erratic at high RPMs. While replacing it, the gasket between the plennum and the throttle body had been sucked in. So I replaced both the gasket and the tp sensor, along with the air idle valve. started it up, no service engine soon lite, idled at 750. drive it 10 miles the idle is stuck at 1500 rpm. Rescanned it, it came up with code 111, system ok! Is it possible that it could have sucked in the new gasket? Sprayed W-D around the gasket and didn't hear any difference. There is no way to manually adjust the idle so theres nothing that out of whack. The throttle cable are fine, even removed them to insure that the idle wasn't effected by them. Any ideas before? I'm sure that this isn't a first, any help would be appreciated.

do check for another intake leak; these did suck gaskets all over the place. However, if this has good miles on it, and it hasn't had the very best of air filtration, then there may be a problem with what voltages the TP sensor is sending to the PCM. Backprobe the wire that goes from the TP to the PCM (the TP signal wire). With key on, eng. off, see what it is.
Then, start it up and using the throttle pedal a few times, blip the gas and see if the voltage returns to within .20 volts of the KOEO (this compares TP running with TP, closed throttle, the basis of what EEC bases its idle strategy off of). If these agree, then there is something else wrong. If these don't agree, then there is wear in the throttle plates that's not allowing the plates to close fully.