You should have an idel air bypass that allows for more air to bypass the throttle body. If it is stuck open the car will start fine and as it warms up the idel will increase. I'm not shure where it's located on your vehical or how to test it but you also need to find out what controles it and test that as well. It may be something simple like a wire off a water temp sensor.

Good Luck
John Roncallo