When Jim and Tawnia are eating at the drive-in, the tray attached to the car window changes. The outside of the car shots show the tray is empty, but when shown from inside the car it has a paper plate and napkin on it.
In the garage where Rockford gets a beat down the guy throwing the punch at him is using his right hand to punch Rockford on Rockfords left cheek. Yet all the marks are on Rockfords right cheek.
Larry Kirkoff's wine changes from red to white between shots.
At the bar where Jim meets Tawnia, the drink left by her male friend is clearly different from the top and side views.
When the cars go off the road to circle back during the chase at the golf course, you can see tire tracks left behind by earlier runs.
During the beginning title sequence Rockford's phone number is seen as 311-555-2368. This same phone number is seen on Mannix's phone, also.
When Rockford is being chased by the semi truck, there is a scene where you can see an eruption of some sort of red fluid from under the center of the front bumper of the semi truck when it rear ends the car. Presumably the trucks bumper was pushed into it's radiator, damaging it.