The other sensors aren't there as spares - it's not a matter of using a backup one. In general, there would be a sensor for each exhaust manifold (so 1 for a straight 4 cylinder engine, 2 for V6 etc) ...

Alright, so that engine knocking and the car running like crap? Yeah, it was back. Even after cleaning everything (EGR, O2 Sensor, Throttle body, Intake Manifold, Exhaust manifold) last time, the ...