This can be caused by a vacuum leak, or the throttle body needs to be serviced. Also, there could be a vacuum line to the IAC motor that has fallen off. Here is a guide to help you find the leak. Please use it when the engine is cold only.
Repair Safety Notice: This information is for general instructional purposes only. Vehicle repair can be dangerous. Verify all information, follow manufacturer service procedures, use proper tools and safety equipment, and consult a qualified repair shop when needed.