The car is an automatic. The check engine light does not come on. Then engine does run smoothly, but it is like the gas pedal is not operating and I'm coasting no matter what I do to the pedal.

I probably did not describe what happens well. When I stop accelerating and want to maintain my speed (say at 50 mph) I can't, the car will start to decelerate even if I start to push the gas pedal back down. This will happen until I come to a stop, and (Without shutting down the engine) press the gas pedal to start backup. It is weird this only has happened when the engine is cold.