I wish the pic weren't so blurry, but the size and general look of the creature reminds me of
the brown recluse.
Do you live in its area of distribution?
Edit: In every case of my personal acquaintances who have seen the brown recluse in their cars or houses, there turned out to be a LOT of them. It if does happen to be a brown recluse I would heartily recommend having professional exterminators make certain that there are no more of them around. They may not be the most dangerous spiders in the world, but they are not a variety with which I'd care to share my abode.
You need a taxonomist, or some such.