actually to clarify to what I said below, they are not sold together. That's only on the Hyundai Accent. Sorry I got confused. Just replace them individually. And this will take care of your driveability problems. The rest are issues of there own. Replace the 02 sensor and check your gas cap. Basically what the other guys said. So now you have 2 people telling you the same thing.

the input and output speed sensor are sold together and are attatched via a common harness. They call them pulse generators for you car. they really suck and go out quite often. when replacing them also clean the connector for the pulse genereators when hooking it back up with electrical parts cleaner and use some dielectric grease that you can get at any local parts store. It's the stuff sold you when you buy spark plug wires and comes in small ketchup packet style packets.