I had a similar issue on another vehichle that turned out to be the IAC (idle air control for the less saavy).
This is a solenoid that controls the amount of airflow to the engine independant of the throttle plate. Thus increses engine air intake for accessories, power steering, etc so that the load on the engine is at a constant regardless of what position the throttle is at.
That being said this solenoid is small motor that drives a plunger into an air passage on the throttle body. If this solenoid is dirty it can get stuck open (air passage is wide open), closed (stuck in the hole thus no air), or in any position in between...
It is very possible to take this off and clean it with Throttle Body/Carb Cleaner, spray a generous amount on the plunger itself and into the hole/passage where it came out of. I have done this in the past and will solve the problem if in fact this is what it is.
If you choose to try this, dont unplug the battery, undo the IAC and plug connected to it (TRY NOT TO MOVE THE PLUNGER MANUALLY), spray it down real good and in the hole, dry it off if you like and place it back in the hole without moving the plunger. Hook it all back up and you are good to go.
Hope this helps