There are a few things you can check. Start simple first. Check ALL vacuum lines, make sure they are all either connected or capped off (i.e. if you are not using EGR then the inlet should be capped off). If all of those connections are good, check your fast idle control valve (make sure the screw is all the way in), then IACV (check for cleanliness), then TPS (make sure its not broken or make sure it is tighened all the way down)then check your idle adjustment screw (make sure it is not too loose, tighten it all the way then loosen it until your idle is sittin where you want it.

If you arent throwing any codes (you didnt mention any) then i would say its safe to say that none of your sensors or valves are broken or not working. My bet is on some sort of vacuum leak.