I've read some about afterfires which are usually caused by unburned fuel in the exhaust, BUT... all I've read talk about modded vehicles. I have experienced this since new.
Although this is like, a couple of times a year, it has always been during WOT acceleration and 1-2 shifting, and sometimes a 2-3 shift. Mine is a 2009 WRX and the first "mod" came after a year with an OEM style K&N filter. Then came a Dynomax VT muffler in the third year, now I've been a year with a KS Tech cold intake. The highest octane around is 91, it's a lucky find to get 92, and there's only one station that offers 93, very expensive here.
My usual fuel is 91 octane and I must emphasize that the first afterfire happened during the first year, completely OEM.
So, I undestand afterfires are not good, but seems to be a usual thing with these engines, correct? But, why when OEM?