if you take your polygonal lasso tool, and zoom in like 400-800% you can fine tune it. Every time you click it will save a point in the selection, so you can click once, then line up the tool, and click again. Go all around the car with that and then go to SELECT then inverse. After that just go ahead and hit your "del" key.
I didn't know if you've tried this or not, but you could try changing the Layer you are on and erasing the Background layer. Hope that helps, if not, Omicron gave you another way.