Check the wire to the sensor 1st to make sure it didn't get melted off or get disconnected. Running rough can be any number of things. How long has it been since the last tune-up? If it's overdue then do that 1st. Check your throttle body intake tube for cracks and make sure all the vacuum hoses are in good shape/hooked up. Check the injector connectors (the ones you can get to) to verify they are hooked up and the wires are secure. If it still runs rough pull a spark plug wire with the engine running to determine if that cylinder is firing. When you pull a wire the engine should stumble and run worse. If it does, then that cylinder is firing. Try that with all 4 wires (one at a time). If you find one that doesn't effect how it runs, then that cylinder isn't firing. If you find a faulty cylinder, check to make sure there's spark at that plug. You can do that by pulling the plug, grounding the metal case while it's hooked up to it's plug wire. Crank the engine and watch to see if it sparks. If it doesn't then it's likely a bad plug, plug wire, or distributor cap. If it sparks then you likely have an issue with that cylinder's injector or it's injector connector/wiring.

One other thing worth noting is compression. If you have a dead cylinder that's got fuel & spark, then there's likely a compression issue. If you know what to listen for you can hear a bad cylinder just by disabling the ignition and cranking the starter. Tim