I have been chasing the cause of extreme surging with this car. It was a bad O2 sensor. So as a quick heads up, most people will tell you its not possible for that to be the cause, but trust me it was. With the new O2 sensor it was running much better (solved the extreme surging) but with some slight hesitation and almost a miss. Later in the day I am pretty sure I found the source of the hesitation/miss... Timing belt that decided to break on my way to show off the car to a buddy. Hopefully the new timing belt will take care of the last remaining problems.
But let me digress, I had a fun time changing the O2 sensor on the newly purchased 1993 Subaru Loyale.
After many trips to the store to grab different tools and things I ended up getting the O2 sensor out.
At first I spent some time attempting to use a harbor freight O2 sensor removal tool but just managed to figure out that its a bit tight to make that tool work and once you have figured out a way to make it work... its a 22mm O2 sensor and not a 7/8 like the harbor freight tool.
Ok run to the local autozone and rent there O2 tool kit (25.99). Throw on the 22mm O2 sensor tool and manage to fight the sensor for another 30+ minutes before saying screw it and removing the whole y-pipe.
Once the y-pipe was out I managed to finish rounding off most the existing O2 sensor and was ready to take to my friends metal shop to just drill it out.
Then I had one last idea, remove the heat shield and see if I could fit a box end on the O2 sensor that way.
Magically it worked. I could fit a 22mm box wrench on the O2 sensor and with some help of a rubber mallet I was able to break free the O2 sensor from the exhaust. It was a bitch but I am pretty sure this was the only way I would have been able to remove the O2 sensor and also the most simple fool proof way to do it.
tl;dr Remove the y-pipe. Once thats free remove the heat shield around the cat. Use a 22mm wrench and a rubber mallet to beat the O2 sensor out of the cat.
Tools Needed: 12mm, 14mm, 22mm, rubber mallet, PB blaster (or something of the sort), rags.
Hope my pain is another mans gain.