97 explorer idle problem

[leafman13]

--------------------------------------------------------------------------------4.0L SOC

i had performed a tune-up a year ago, and the truck ran great. then it developed a missfire which was a bad plug. i replaced the plug and at the same time cleaned the throttle body which was really dirty.
after that the idle problem started. during warm-up it idles at 2000-3000 rpm, then drops down to 1000 after warmed up. as soon as you put it in gear, it goes up to 1500 and will coast down the road at 40 kmph with foot off pedal.
it will go down to 1000 in gear and if you put it in park it goes back up to 1500. i dont think it is the ilde motor because it is doing what it is being told to do, also i tried a used one and it did the exact same thing.
i tested the TPS sensor with a snap on vantage and the votage is correct and constant. as for a vacuum leak, it would be strange to start this prblem after cleaning the throttle body.

any ideas?

 

[2000StreetRod]

Throttle open

. . . during warm-up it idles at 2000-3000 rpm, then drops down to 1000 after warmed up. as soon as you put it in gear, it goes up to 1500 and will coast down the road at 40 kmph with foot off pedal.
it will go down to 1000 in gear and if you put it in park it goes back up to 1500. . . as for a vacuum leak, it would be strange to start this prblem after cleaning the throttle body.

Vacuum leaks allow unmetered air to enter the engine resulting in a lean mixture (low idle speed). For your engine to idle at 3000 rpm, metered air is entering the engine. Either the air is coming thru the IAC valve or the throttle body. Try disconnecting your throttle cable and then make sure the throttle plate is closing fully. Make sure that the throttle stop adjustment screw is not preventing the throttle plate from closing. Dont' adjust the screw to make the throttle plate close so tight that it sticks when you try to open it. Then start your engine with the cable disconnected and see if it still idles fast. If so, then I suspect the IAC valve is excessively open.