The ambulance that K.I.T.T. and Mr. Knight chase alternates between one with a siren upon the roof and one without a siren upon the roof (indicating two vehicles).
KITT is hydroplaning on the Fin Quest's starboard side. He disappears when Michael throws a henchman over the same side. Additionally, KITT would have run over the man had he been there.
After Michael thwarts the attempted poisoning at the hospital and the villain runs out, Michael chases after him and uses his wrist-radio to tell K.I.T.T. to meet him outside. We hear K.I.T.T. start up, but then we see his gearshift move from "D" to "R". There are two errors with this:
(1) If K.I.T.T. had been parked and with his engine off, his gearshift would have been in the "P" position before he started up again.
(2) Cars with automatic transmissions have a "neutral safety switch" that prevents the engine from being cranked unless the transmission is shifted into either "P" or "N". So K.I.T.T. could not have cranked his engine if his gearshift was in the "D" position.
When K.I.T.T. picks up Michael at the back entrance of the hospital you can see tire marks from previous takes.
The ambulance with Bobby's would be assassin is already overturning when it hits the truck and explodes.
The same establishing shot of the hospital -- an ambulance passing two nurses before the camera pans up to higher windows -- is used twice.
K.I.T.T. picks up Mr. Shell on sensors, saying that there is a life form in distress at 3 o'clock. In directional terminology, '3 o'clock' is 90 degrees to the right; Mr. Shell was to the left of K.I.T.T.
While the candles in the sea cave are atmospheric, they're illogical. They certainly hadn't been left burning, and Jennifer would likely use a flashlight or portable lamp.