Continuity mistake: During the car chase scene near the end of the movie when Connors jumps on to the black car the windshield is only slightly lowered. Later during the chase the gap is much bigger and when we see Callahan struggling in the back seat it's lowered all the way down. Also, Connors grip on the car keeps changing between closeups and far off shots.
Continuity mistake: When Lt. Talinsky and his fellow Russian officer arrive to the warehouse in the yellow car, we see Talinsky in the passenger side of a left-hand drive car and in one shot when the car is spinning, he's now sitting in the driver side (as if the film was flipped). We also see shots of the car with the window rolled up and close up shots of the window rolled down.
Continuity mistake: When the American and Russian police officers arrive at Konali's warehouse in the police van, shots inside the van you can see the window curtains closed, even the back one. On outside shots, some of the curtains are opened, most noticeably the back one. The clearest example of this is when the van is spinning out of control.