I have done a lot of reading and research on the issue, and I'm not seeing anyone with the exact issue I am having.
I have had one problem after another with my Legacy with 123k on it. I bought the car and shortly after, had a slightly rough idle from a minor misfire. the issue increased and I am now stalling out when the car is in drive at a stop sign. I was getting 3 misfire codes, and an EGR Temp Sensor code. In an effort to see if the temp sensor was the cause of the issue, or if the issue was the sensor, or something else, I read on a WRX forum that said you can unplug the sensor and connect a 2.4k ohm resistor to make the ECU thing the sensor is working correctly. now I have no EGR code, but it's still throwing misfire codes on 3 different cylinders and runs just as badly as it did before. I already tried replacing the plugs with the good NGK plugs (which I was told do NOT require gapping, and can be damaged if I attempt to gap them... right?). I have no coolant in my oil. I have lost about 4 MPG in fuel economy. the car is running super rich. it also runs smoother when the car is cold. the misfires go away once I get above 2k RPM or so.
Before I put a resistor in it, on 3 different occasions the car completely stalled out on me at the bottom of a large hill near where I live. it happened right as the engine started to warm up. it would crank and crank, and eventually start, but if I would give it any gas at all, it would die again. park the car. let it sit for 2 minutes, start it, and it's fine (apart from the usual misfiring).
May also be helpful to add that I blew the turbo and had to replace the center section on the turbo 2-3 months ago. since then I have a "squirrel" in my turbo any time I generate boost. I have yet to take it apart and investigate what the issue is there.
Thanks in advance for your help!