If it does not stop on the "Air" and "Timed" cycles then the timer has to be replaced.
If it does not stop on the "Regular" and "Perm. press" cycles only then I would recommend to check the timer resistor resistance first. It should be between 4050 Ohms to 4950 Ohms.
- The part number for the timer is
AP2997394
- The part number for the timer resistor is
AP3094277
Here are the break down diagrams for the Whirlpool dryer
Model LE9300XTW0
Gene.