Check the idle control valve on the throttle body. They tend to carbon up and if you remove it and clean it where it goes into the throttle body with a good MAF or other cleaner your problems will go away. You will have to remove the throttle body to do this.... a good idea anyway because this way you can clean the whole throttle body out with the cleaner. Been there......done that...... it should help greatly.
+1
You would not believe the build up you can get on this thing. As said, MAF cleaner and a soft cloth will do wonders. Not a bad idea to gently clean the valve's ports on the throttle body too, as those get just as carbonized.