Ford Repair: High Idle Problem, 1993 ford 4x4, vacuum leaks

Question
I have a 1993 Ford 4x4 F-250 351 EFI. I'll start the truck and the engine will run at 1000rpm. I'll then proceed to put it in drive and start to drive when i stop at a stop sign the truck is at 1000 to 1100rpm Then if I put it in park or neutral the truck screams between 1200rpm to 1800rpm and won't drop back down but sometimes i'll turn off the engine when its doing that and start it back up and the engine will idle fine but soon as i drive it for a bit the rpms will go up. it makes it hard to stop at a stop sign if the engines at 1100rpm in drive because it wants to keep lugging forward.I took it to a repair shop and they changed the tps switch, idle control motor, thermostat and they said their were no vaccum leaks. I also had the air filter changed, rotor and cap changed a oil change done and the problem still continues. They said thay hooked the truck up to the scanner but it didn't show any fault codes. In retrospec they can't figure out the problem. Please help. Thanks for your time.
              Dan

Answer
The idle control valve sticking would have been my first choice.

After replacing this valve, you have to clear the PCM memory, otherwise it remembers the previous idle strategy and most likely will continue the higher idle until it can relearn while driving. To relearn the PCM, disconnect the battery for 5-10 minutes, reconnect and let the engine idle in gear, in park, with and without AC on, for 3-5 minutes each. This should "reprogram" the PCM to the correct idle.

As long as there are no vacuum leaks or other problems this should work. This engine had problems with the throttle body gasket, intake plenum gasket, and EGR valves leaking. Also make sure the throttle isn't sticking, either due to a bad cable or a sticking throttle plate.