One clue? "replace A/F sensor (OEM from Subaru dealer) last year when the light first came on. Ran okay for a few weeks, then misfire codes came back"
So, the o2 DID fix it, if only temporarily???? This probably means something to a Mech/Tech expert.
- Fuel injectors...check resistance. I don't know what it should be for your year...those are Top-feeds, correct? No, it's not likely that all 4 are bad.
Cause of P0172:
Faulty fuel injectors leaking fuel into the combustion chamber
Faulty spark plugs
Faulty manifold absolute pressure sensor (MAP)
Faulty throttle position sensor
Dirty or clogged air filter
Vacuum leak
Faulty ECU (or PCM module)
Faulty fuel pressure regulator
Faulty thermostat (stuck open)
Cooling system that’s been retrofitted (ie: thermostat removed, fan running direct, etc.)
Restricted or damaged fuel line
FWIW:
If 'throwing in the towel' means selling for a loss....then how much is it worth to have a Reputable Subaru Shop (not a dealer) check it out?
Drop a $200 for a diagnosis>>fix vs. lose $1K or more because the CEL is on?
Of course you live in the PNW, so Subaru Central..... peeps probably come up to you on the street with offers...plus the overpriced PandeMarket.