Twice in a row, when I've taken a trip to Yosemite in my 2004 Prius, the M.I.L. light has come on. When I take in for service, the scantool says cylinder one is misfiring. The first time around they found some corrosion / water damage as specified in some TSB, but this time around they can't figure out what's going on. The only thing I can think of is that both times it happened when 1) it's cold and 2) the car is at altitude. Anyone else experiencing something similar?
tell them to change the spark plug in #1 hole. You probably had water in the spark plug tube and it shorts out the plug. Irudium plugs don't really like miss firing and quite often fail shortly after a few misses. The other thing that happens with miss fires is the cat's can't take the load of fuel dumped in them and they over heat and could have a core meltdown, plugging off the exhaust. This needs to be addressed as soon as possible.
the ignition is a COP (coil on plug) suggestion: swap coils, see if the misfire moves to the other cylinder. well, maybe it's a suggestion for the tech if you're not comfortable tinkering under the hood.
