This engine was running flawlessly. On a fairly long
highway trip, it started to misfire. By the end of the
trip I am pretty sure that there were two or more
cylinders misfiring. Please note that I had never
experienced *any* misfires before this event. I
want to make this clear because I think this
diminishes the likelihood that plugs are involved,
although the plugs have not been changed in
some time.
    Plugs are very expensive to change in this
car and only the dealer will change them. As
the car has 150K miles on it and has other
non-engine problems, I am trying to avoid
spending money needlessly. If possible, I
would like to examine all the less expensive
possibilities first, ruling out everything but the
plugs before I "bite the bullet." (Around $400.)
    Could someone list all the other possibilities
that might be making this engine misfire on
multiple cylinders, and that could cause this
to occur suddenly?
    Many thanks for your help!
          Frank