Power fc English manual?

[L18M]

my understanding is you need o2 sensor as that measures if the air/fuel mix is lean or rich.
unless theres another way of measuring if engine is running rich or lean?

on my legacy the o2 sensor needs replacing and from the wrong o2 reading.. it prevents the primary turbo boosting properly as the fuel / air misture is not right so the ecu takes this into account and adjusts everything else depending on the dodgy o2 reading.