Is the code Po306 cylinder #6. An engine misfire can be caused by engine mechanical isues, fuel issues, or ignition issues. You've got to start with the basics, check the engine is mechanically sound (good even compression, no vacuum leaks,valves are properly adjusted (in the case of shim or screw adjusted valve clearances, your engine has hydraulically adjustable valves so this is not applicable) check the engine's ignition system is good (good spark plugs coils or plug wires where applicable) then the fuel system needs to be tested and inspected to make sure it is operating efficiently. A misfire can be caused by many things but basic diagnostic tests need to be done rather than just trying to guess what the problem is. There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online
A professional grade scan tool may be needed it allows key engine sensor data to be analyzed right off the scan tool without having to do intrusive testing at each sensor.
to add to Pat. I would start with a compression test. After that, I would go to have the cat converter checked. if you drove for a long time with a engine miss, you may have damaged the cat converter.