1989 Chevy coversion van always idles too fast. Why?

[Paul]

I have a 1989 Chevy full-size van, 350FI, and ever since I bought it, it idles like 1200-1500 rpms, if I drive it somewhere, and let it sit and run 10 Min's or so, and put it back in gear, it will finally idle down, then if I shut it off, wait 5 Min's, it will idle fast again for a long time. The colder it is out, the worse this is, Im totally annoyed by this, and have been around cars along time. Even after it has idled down, if I drive it down the highway, it will be idling fast again. What do I need to look at, thermostat is the correct size,

 

[bandit_60]

sounds like the idle air control sensor or the throttle position sensor. it could also be that the throttle body needs cleaning.

 

[Perna00]

idle air control valve and vacuum leaks.