HelloCustomerand welcome to JustAnswer.
If the car runs worse now because it was damaged by the repair shop or they negligently repaired it improperly, you would have a cause of action for either the return of the money you paid for the repairs, or for the cost of repairing the damage they did, or both.
That said, it would probably be very difficult for you to prove that they caused the problem. At the very least, you will almost certainly need an opinion from another repair shop about the negligence of the first shop in working on your car.
Before doing anything else, you should see what the repair shop has to say when they look at your car again. Every now and then, people will actually own up to their mistakes and it could happen here.
If it does not, and given the likely total value of your claim, this would be a case you could file in small claims
court and therefore you will not need an attorney.
Thanks for asking your question here on JustAnswer. If you have any other questions, please let me know.