Last Fall I replaced the plugs and wires on my metro. Since then I have had 1 plug go out me about once a month. It is always the same spark plug. I've cleaned the rotor, but haven't replaced it. What is the problem?

What color is the plug? Is it fouled out? or burnt up?

No, The plug is pretty clean when I pull it. It is black there is no carbon or anything.

If it's black, it's most likely running rich. You may want to upgrade the ignition coil, or replace the cap and rotor or both. Also, check and see if your ignition timing is ok.