Do you have a K&N filter in there? My car did this for a while. I had the IAC valve replaced and it still did it. Finally Lee Cox told me to check my K&N filter and see if it was over oiled. Sure enough it was. Sometimes they seem to come that way from the factory. I ended up have to take it out and clean it and all the parts around it. Problem Solved! Not sure if this is your problem, but it wouldn't hurt to check!
