My picks aren't movies, but I've always loved the cars in both
Columbo and the
Rockford Files; the titular Columbo drives a Peugeot 403 Cabriolet! How many of those could possibly have existed, even at the time, in the US?
Anyway, both take place in 1970s Los Angeles with all the far-out automotive subcultures that encompasses: burnt-out hippies, chainsmoking Cadillac backseaters, stringback glovesmen, thrifty and pert little Japanese runabouts, the Mercedes country-club set; they've got everything.
I can also heartily recommend them (especially
Columbo) as good TV, which car-centric content often fails to be. The pacing, like the cars, is very '70s: British fans of
Morse will recognize the walking pace of the show as clues are deliberately and artfully collected and ruminated upon. It's an especially-pleasant antidote to the gunshot!, car-chase!, semen stain! style of cop procedural that seems to have been king for the last twenty years...
The Rockford Files leans a bit more in that direction and crunches Pontiacs with gay abandon (even though they weren't yet
falling out of railcars onto TV sets...), but I still find its canter to
Columbo's trot gentle enough.