Unfortunately, the question is a little general for a specific answer..
There are alot of great car illustration tutorials out there.
But yeah, definitely check out Jeri's tuts. She rips.
On a semi-related note, most tutorials can only show you how to twist a wrench.
'art' or 'vision' or 'whatever' must come from within. Tutorials teach mechanics.
Inspiration is much more illusive.
.02 for the topic.
Cheers man.
Hope you find what you seek.