And it should also come with a carcols.dat line. Now for the handling - usually almost every modded vehicle comes with a handling.dat line AND vehicle.ide line. I converted it and at the end of the line it says (example) sports+ext_rare you want to delete ext_rare. If it is low like under 10 you can rise it up a little bit (just watch it setting it over a certain # can cause your game to crash if your processor doesn't have the ''guts'' to run the game with so many cars spawned).

Open vehicles.ide with notepad and look for MaxNum (of your replaced vehicle or the vehicle that rarely spawns).