The first thing I would do is to read the computer error codes. A cheap scanner for about $30 can be purchased at any auto parts store or Ebay or you can use a meter. This small investment has saved me hundreds of dollars in repairs. You could also pull off the idle air control valve and check/clean any sludge out of it. Should look something like this.
http://www.partsamerica.com/product_...e/NIE21760.jpg
Wiring to same needs to be checked also for chaffing. Next be sure you clean out your throttle body in the area right behind the throttle plates. Pick up a can of special cleaner at the auto parts store. Hope this helps a little. Regards-Stevo