Revealing mistake: When KITT is in the valet carpark, he pushes the cars in front of him forwards. It is very obvious they have attached rubber protectors to the bumpers to prevent damage. Also, when KITT is driving by himself 10 seconds later, you can see the stunt man's hands driving the car.
Continuity mistake: When KITT drives off the edge of the cliff, the car changes from a pontiac to another standard car a number of times. When KITT lands, his flight trajectory was from approximately 10 feet, not 100 feet. He should have landed like a belly flop onto the sand, not a shallow dive.