It may be the IAC. They are pretty common problems especially as the weather cools. It consists of a small electric motor(just a little bigger than an toy electric race car motor) attached to a plunger. It's located at the end of the air intake duct at the top of the engineunder the engine cover. It's undone with 2 bolts and a 2 wire connector. If you clean the plunger area out it should fix your problem if the IAC is the culprit. I flushed the plunger area with engine oil. Pour it in the top area of the plunger and let it flow through and out the bottom. If the plunger appears stuck shut, you can gently open it with a small screw driver. When flushing, hold the motor end up so oil runs away from motor. Mine has been running just over a year since I cleaned it. I'm planning on flushing it again before the extreme cold sets in. Easy job. 15 minutes
If you choose to replace, they run anywhere from $55.00 - $85.00 so shop around.