I'd hope its your octane level. But you have a laundry list of problems.... I'd try to give it back, but the car sales industry is a vicious mofo.
Lemon law is really applying to manufacturer warranties, only some states have subsequent laws for used cars.
Check this article from edmunds, some good info! Its from 2009 so things probably changed.
A New Twist: Used Car Lemon Laws
The frequency and severity of consumers' used car problems has led some state legislatures to pass new laws. Currently, though, only six states, Connecticut, Massachusetts, Minnesota, New Jersey, New Mexico and New York have lemon laws on the books. The laws provide a statutory used car warranty, often based upon the age or mileage of the vehicle. If the vehicle exhibits problems during the warranty period, the dealer is given a chance to repair them. If those fixes don't work after several tries, the dealer usually must either replace the car or refund the buyer's money.
At least seven states have some other form of used car buyers' rights, requiring used car warranties or setting minimum standards for the sale of used cars: They are Arizona, Connecticut, Illinois, Maine, Nevada, New Mexico and Pennsylvania. Still other states, including North Carolina, have an Unfair and Deceptive Practices statute that can be invoked. But only those states with true used car lemon laws require the dealer to provide a replacement or refund for your car.