ok so just to start off i know that my truck idles high at start in the cold now the problem then my truck starts it idles smooth but after driving a little while when i put it is park or N the idle is high low high low it is like it can not decide if it was to stay at cold idle or not WHATS wrong lol i have no clue
this truck has never done this in warm weather

FYI my truck is 1988 Toy v6 EFI 4x4 if you need any more info let me know

 

i would guess the cold start injector is having fits. mine just got stuck open the other day and i had to unplug it to get my truck to even start. thats just my best guess from your info provided

 

Coolant temperature sensor, or cold start injector.
Mine did this with the Coolant temperature sensor, 20 bucks from autozone and i was good to go!

 

Air is trapped in the cooling system. Coolant is low. Head gasket is leaking into the cylinders...