PMP 600

The PMP 600 is a 4-door car featured only in Grand Theft Auto IV. It resembles a Chrysler 300C. The car's brand is called Schyster, a spoof on Chrysler; also, PMP is a spoof on pimp.

Locations
There's one in the alley by the Exchange District Bank in Algonquin. All around you will find them, as they are a very common car in Liberty City, especially in Algonquin.

External links:
Chrysler 300 on Wikipedia