i run a car forum too, but its kind of dead also, i admin on another forum and have just reskinned it. There's pleanty of car forums out there and IMO the irst thing you need to do is get it looking good and then work out CONTENT. Content is the key to any site i remember when i started my site i just posted anything and everything to do with cars just to make it look like the forum was busy, unfortunately i thought the forum would continue to grow, and i had to take a few months out due to work commitments, when i came back the forum was dead.
Just showed me if i wasnt there and didnt post, no one else was going to bother.
If you want some more tips just PM me