The four-wheeler used in the theft of the explosives had "Bob's Plumbing Supply" on each front door. It wasn't there when Michael and KITT were chasing it and got hit by the power lines wiping KITT's memory. It was then back when they got to their secondary vehicle.
When Doug first encounters K.I.T.T. and K.I.T.T. chases him down the road, the hooded stunt driver behind the driver's seat can clearly be seen through the rear window.
When KITT is electrocuted and the transformer blows, the subsequent shot of KITT wrapped in cable is clearly a model car - the hubcaps are missing their texture and the rear spoiler is larger than normal.
When KITT is jumping the ravine, something resembling a leather cloth is hanging out of the passenger window. After landing, it is gone.
When KITT proceeds to disable the bomb, the footage of the timer is clearly superimposed over a static background image - this is evidenced by the background image wobbling slightly and the timer display staying still.
When KITT tints his windows to hide Doug, it's obvious it's a camera dissolve between un-tinted and tinted cars. The two shots don't line up exactly.
When Doug uses Turbo Boost to jump KITT over the ravine, the footage of the jump is clearly recycled footage from THE TOPAZ CONNECTION.
In the ending scene, it can be easily notice that the dashboard of K.I.T.T.'s is not the one which is used in series third season.
Jeep Cherokee Chief when nitrous was used sounded like it was manually shifting gears but it was an automatic and the driver always had both hands on the wheel.
After KITT is electrocuted and he drives off automatically, the cameraman is reflected on his door.