I noticed the igniter was remaining glow this morning, but the burner and fan were off this morning. I turned offt the thermostatic and the power from the furnace an hour. Then turned on the furnace again. The gas burners light up after the motor started ran and the igniter was glowed for a few second. But I can see the igniter remain glowing even the gas was shut off from the burner and the fan was off.

The model is Trane xl80

Sounds like a bad igniton control module. Trace the wire back from the igniter, and where it hooks to will be the board or module that needs replacing.