When its cold outside the car will start good.

With high idle, block off mouth of throttle-body, see if it effects the idle. It should kill the vehicle. If no effect on idle, you have a vacuum leak/false air getting in there from somewhere.

Any applicable trouble codes? You should be able to check for codes, yourself. Use jumper wire at A & B terminals on the datalink connector. Turn key just till the dash lites come on, no further, no crank. Then the mil starts flashing, you count the flashes to get the codes. Your looking for two digit codes.

Check/ clean the idle air system.

Let us know what you find.