MTyoda

I have an 89 22re pickup and when the motors stars cold it idles around 1200-1500 and calms to about 850 once warm. Now if i shut the truck down say to go into the store for 5-20min and start it back up it idles at 5-600 until i drive for maybe 2min or so it goes back up to 850. I just dont know what this might be.
thanks