High Idle in park and Drive

1995 Rio Grande with the 2.5l. When it starts it goes to 3k and slowly backs down to 2500. When I’m drive it stays at 2k. Any ideas?
Idle air control (IAC) valve maybe got stuck open or isn’t operating as the computer is telling it to.
 
I agree IAC is not correct. I put a holly sniper on my 2.5. And had exactly that…..The IAC is displayed on the consol…… pull your plugs, may be running way rich. You may need to clean them. That’s what happened to me when I first installed my snipper until I got IAC set up correct….I know snipper is not what you have, concept is the same.