I have a 2002 wrx wagon.
At 30K I had to replace spark plug #2 because of misfire. At 62K I had to replace plugs 1 and 3 again because of misfire (odb2: P0301, P0303). The plugs have carbon soot. Incredibly the two plugs failed within minutes of each other. I was able to limp home on two cylinders.
I also tend to drive at low RPM (most of the time around 2000 RPM) and often drive short trips. I understand this contributes to the carbon sooting.
photos of failed spark plugs
If I rev the engine to 3000 rpm for a few seconds at the end of each short trip, would that help? According to NGK web site, hotter temperature is required to burn off the carbon soot.
In the future, is it advisable to use a plug with hotter heat range? The OEM plug is NGK PFR6G, perhaps I should try PFR5G?