My car is running very poorly when I start my 1994 Buick Century for the first time every day. It will stall out especially at a stop, but starts right back up and it stutters. Plus, the service engune light is on and stays on until I stop and restart the car. After 20-35 minutes of driving, after I park, it will run better if started within approximately an hour. The service engune light is off and it will not sputter and stall out then until it sits longer. Usually about an hour this happens each time I drive the car. Can anyone suggest what's going on?