I"ve owned a few Subaru Legacys of the 1990’s. A common problem is intermittant camshaft and crankshaft sensors, particularly “cold”. Symptoms: engine turns over but no ignition; then a few cylinders fire. Over several minutes, three cylinders (which runs but poorly); then all four. With warm engine, no problem. Usually happens after 150Kmiles with me. A misfiring engine might generate odd error codes - don’t know if bad cam/crank sensors produce codes as well. But you might get some old sensors and carry them around, in case they DO fail.
I just wanted to say a big “THANK YOU”. I came across this set of posts while researching the same basic problem w/ our '93 Subaru and it solved our problem.