it sounds like the coils are bad, rx-8 coils are notorious for failing.. coils are what fire the spark plugs, even if you replaced the spark plugs, if the coils are bad, the engine will not run or run like crap. new coils are $30 a piece, and there are four of them
http://www.oreillyauto.com/site/c/se...004&make=Mazda
i am in Charleston, i could take a look at if for you, send me a pm