When I brought home Charley at twelve weeks old he was sick in the car. He was sick the next time we went out, and he refused to get in the car and would run away when I opened the garage door.
I solved the problem by not feeding him for some hours before going out, and I would make very short journeys to take him out for a walk. When we arrived, and he wasn't sick, I gave him a few Doggie Chocs which he loved, and I would make a big fuss of him. I continued this for some weeks, going out every day. It took about seven or eight weeks of this and Charley loved to go out in the car. It was obviously psychosomatic. His first journey in the car made him sick so he associated car travel with being sick. He was never car sick again, and we would travel to Souillac in France without any problems. Indeed, he loved going in the car.
Try this and I'm sure you will solve the problem.