1992 Buick Lesabre Service engine light

1992 Buick Lesabre 60,000 miles

When I start the car up the service engine light lights up. It stays on for 2 minutes and then goes out. The following day the same pattern. Start the car the light goes on then in 2 min it goes out. The car runs great all the time. Though the air cond is not great

I could live with it because it runs so well but it is anoying for 2 min.I have changed the gas cap already