Does he sleep right away in the car? It might be he's not getting enough sleep, you would think removing naps during the day would make nighttime sleep easier but it's the opposite, you might want to increase the amount of sleep he gets during the day, then he's not overtired.
Since he's so old I think anything you try is going to be tough; we never did the cry-it-out thing but a softer gentler version of it, but we started by just making sure he could fall asleep by himself without us in the room at 3-6 months.
If you can't handle the cryitout way, what I did is I would go in and console him or do whatever to get him to calm down, but slowly I would remove it. So for example I would start with the usual pick him up and hold him till he's almost asleep, but then I would hold him less and less.. I would put him down, he'd cry, I'd pick him up, he'd stop, I'd put him down, etc etc.. after 30 times eventually he got it and stopped crying.. then when he'd cry I would go into his room and just put my hand on his back instead of picking him up. Then just go into the room. Then just shush him from an open door, etc.. It took me weeks and weeks and weeks just to get rid of one nighttime waking but it worked.. might have been faster if I just let him cry for more than 5-10 minutes, but that was about my limit.
Read books, check parenting websites, every kid is different and it can be tough to find what works, but for us we decided early on that good sleep habits were the one thing we wanted to make sure we did well, and it worked out good; he's got really great sleep habits now (he's almost 4).