You have a dirty IDLE AIR CONTROL VALVE. This usually happens over time and with the use of cheaper dino-based oils. Vapors collect here, and inhibit the proper functioning of this vital engine controller. You can fix it yourself using the VECI map under the hood and a can of Gum-out spray. Clean your throttle body and IAC valve to showroom clean, and KEEP it that way. For even better results, remove the factory spark plugs, and install a set of Bosch Platinum or Fusion plugs. You will get more MPG's and better power by about 20%.