When KITT is about to leave the semi, the sun roofs are both removed. Next shot, when he is driving down the semi's ramp to get to the road, the roofs are both installed.
Between shots when leaving the school and the "race", conditions quickly change from overcast and wet roads to sunshine and dry roads - and back.
When Katherine tries to escape up the hill, one of her blue shoes falls off before she rolls down the hill. When Michael catches up with her, she's wearing both shoes with no time to have picked it up and put it back on.
You can't check a pulse while wearing thick gloves as seen at the beginning.
When Michael takes Catherine from the party, just as he's driving away and Scott comes around the corner on foot, Scott criticizes KITT for being domestic. He then proceeds to get into an Avanti II to give chase. The Avanti II is also a domestic car.
Obvious stunt doubles for Michael Knight and Christopher Stone during their climactic fight.
When Stone persuades Katherine to flee the Foundation, he asks her to meet him on the corner of Aberdeen and Vermont. Aberdeen intersects Vermont at its beginning and its ending, about a tenth of a mile apart. Stone did not specify which of the two corners to meet.