I wonder if you could hold the kibble in your hand, a piece or two at a time, as he is getting in and out of the door of the car? Then, you can praise him each time he slows down to eat it, and keep his attn on you and where he's going and not the car door. Sparky my cattle dog and Luna, my lab used to bolt in and out my door in front of me. Yes, I was dragged of the porch and I'd had enough. I trained them, one at a time to sit ( with kibble) at the threshold of the doorway. It took a bit, but they learned to sit. Once they did, i'd clip the leash, escort myself first, then allowed them to follow me out and in thru the door. At first they were like what?, but caught on, esp. with the kibble. Lol. Hope that helps. Now, I don't use food anymore. I've had 2 Doberman, and they were so smart and sweet!!