The car runs good, no problems. Spark plugs are old, 150,000 miles and 16
years (1997 vehicle).

I decide to change the plugs. No troubles BEFORE I begin.

When I am done, the engine runs poorly, severe -- or at least notable --
misfire. I drive for a day or two -- probably about 50 miles or less --
until the check engine light comes on. I pull codes, a single cylinder
misfire. No big deal, I discover the plug wire not seated well on the plug,
easy to cure.

Engine instantly runs better -- misfire is gone.

Now I am driving around with the scan tool connected just to be sure that
the things I feel in the seat of my pants don't turn into a fresh round of
engine codes. I don't feel much, and no misfire reports. Life is good.

Hold your horses, life is not so good.

I have a Pending Code, P0430 CATALYST BELOW EFFICIENCY BANK2. The check
engine light has not come on yet, but if the problem is true, then it should
come on in a few more drive cycles.

My question is, if I have a misfire will the resulting raw fuel damage the
CAT or the post-CAT sensor? I was not aware that a misfire could take a CAT
out. The misfire that I had is in Bank2, so there is a correlation between
the misfire and the new code.

Of course, there is a strong possibility that the plugs I installed are not
the right ones -- just because the parts guy says that the catalog calls for
them does not mean they are right. After putting the plugs in, I went to the
dealership to get the factory plugs and plug wires -- $230 for plugs and
wires from the dealership, ouch! -- but have not installed them because the
engine now feels just like it did before I started working on it. (Curing
the misfire code fixed the poor operation, entirely, so I'm in no hurry to
open the hood again. It was very difficult to reach the plugs, and if the
engine runs then I don't want to do the job over again.)

So, my question is if I damaged my CAT or if it is merely a coincidence that
I have a P0430 Code in pending status?