The HC shows that his vehicle is reluctant to burn the expected amount of hydrocarbons before they exit the tailpipe. A new cat will most likely fix that problem. Most people will do a full tune up before they go that route though. Not like it would be a bad thing anyways, but it is a process of elimination. Here is my checklist.

1. Have you ever used or race fuel, octane booster, fuel injector cleaner etc? This stuff can coat your cat and make it lazy to burn all HC's. A good tune up still may not help get your car where it needs to be, so replacing the cat will be a must.

2. If you have not used additives or race fuel:
3. Replace the cap and rotor.
4. Replace the spark plugs.
5. Check the wires for crappiness and replace if needed.
6. Replace the fuel filter.
7. Adjust the valves and timing if needed.
8. Change the oil.
9. Clean your air filter.
10. Heat up the cat real good.
11. Take your car to the station and cross your fingers.