My 4 year old son was diagnosed with pddnos which is on the Autism Spectrum... He also only loved playing with cars but he would do a lot of mimickink ( forgive my spelling) things he would hear on TV even though it was in the right timing. We were concerned because his speech seemed delayed but we could understand what he was trying to say. We had him evaluated by a group and we are here in Texas. It is called ECI- Early Child Intervention. He was then diagnosed and we started him in a program at our local elementary school and has been in it ever since. I am hoping that your kido does not have any of these issues but please know if he does there is help and my son has made huge improvements and the goal is for him to be integrated into a regular Kindergarten class and be out of special needs. Good Luck but I would get him checked out if you have any concerns!
The diagnostic criteria for autism include delays in communication and social interaction skills, and restricted or repetitive behavior. In addition, these patterns of behavior need to be observed quite early to qualify for an autism diagnosis. Other autism spectrum disorders (Asperger's, Pervasive Developmental Disorders, NOS, etc.) are diagnosed based on similar characteristics.
Based on your description, it's tough to tell whether he actually meets any of these criteria - your description of his development in these areas doesn't really seem that extreme. Also, remember that there can be quite a bit of variation in what is considered typical development. However, only a professional (a pediatrician, psychologist, etc.) doing an in-person evaluation can determine whether a diagnosis of developmental disabilities is warranted. I would recommend that you take him to the pediatrician and explain your concerns, and s/he can help decide whether referral to a specialist is warranted. This way you can either rest easier knowing that someone has ruled out a diagnosis, or you can get your son started with some intervention.
Best of luck to you