Jon refers to a black 1978 Corvette as a 1977.
Melodie is wearing completely different clothing when she breaks into Ponch's car and then when she drops the car off minutes later.
At the beginning, when Ponch wrecks his bike, he not only doesn't get any cuts or scrapes on him, but his uniform is still spotless, with no tears or even dirt anywhere on his uniform.
When Randi Oakes was at the TGI Fridays, she was not wearing a bathing suit too under her clothes. You can tell because the bathing suit top tie that goes over her neck would have shown. Second, she was obviously not restricted in her movement when walking.
In the shot of the Lincoln driving into the water you can see that there are no people in the front seat.
In the opening chase scene when Ponch crashes his motorcycle, you can see that its a stunt double doing the crash scene.
There's no reason for Kim and Melodie to speed away like crazy, leading to the police chase and drive into the water, after seeing Ponch and Jon at the restaurant.
When Kim is talking to Melodie in the car, she refers to Ponch as the "talkative one on the left." Jon was on the left, Ponch was on the right.