Different states have different laws. Call the District attorneys office and ask them where you can find out about the laws that apply to you. Not to be pessimistic but let this be a lesson to you. You should have had a mechanic look at it before you bought it. In the future, always get a carfax before hand and look into any recalls on the vehicles you're interested in. If the seller tries to discourage any of these things, keep looking. If they're not trying to hide anything they shouldn't have a problem. If you still have the ad, and it say's it's "perfect" and you can prove otherwise, you may have a case. Especially if you can prove the seller knew otherwise. Most states have disclosure laws.
Good luck in future car buying ventures.
Oh yeah, when buying a used car, make a list of all the things you want (A/C, power windows, cd player, color etc) and all the necessary things (like under 100k miles, clean carfax, good maintenance records etc...) Then look for a car that has all these things. If it doesn't exist, compromise, but ONLY on the wish list. A car with 201, 000 miles and a killer stereo system will only get you so far.