Check the curb idle speed screw. When cold, your engine will be running on the fast idle speed screw. You can test this by taking your car for a drive until it is warm, shutting off the engine, open the throttle and move the choke back to the closed position so the fast idle screw is on the cam, and then start it without touching the gas pedal. If it idles fine, press the gas pedal and release and see if you lose your idle. If so, adjust the curb idle speed screw.