When I first got my dog, she jumped eagerly into my car, to escape the abusive hell-hole she lived in. I stopped a number of times during the 8 hour ride home, for her to pee, etc. and each time she leaped into my car.
BUT,after I had her a few days, and wanted to take her out in the car, she didn't want to get in. I really think she was afraid I wouldn't bring her back.
What I started doing was taking her for VERY short rides, like around the block, then right back home again. I swear I could see the relief on her face when I opened the car door!
Dog who have been passed around a lot can freak out this way. Although my dog didn't misbehave in the car, it was upsetting to see her so miserable.
She still doesn't jump in eagerly, but I have no problem getting her in now.
For your dog, you need to go one inch at a time. I wouldn't even try and get him in the car for now. You've had him a very short time and he is probably insecure. He needs to get used to the routine of the household and feel secure before you start taking him places.
When you do start working with him again, get him in the car, with his toy or whatever, then just sit in the driveway til he calms down. Then take him out and go back in the house and praise a lot if he has been good. Repeat the next. Wait for him to calm down, praise and/or give treat. Get out. You want him to think that getting in the car is kinda boring.
Eventually you can turn the engine on....go for halfblock rides, etc.
This can take some time so don't try and do it in one day as that will stress him out completely.