Hooked up my car to HP tuners,
saw my 02 was adding fuel and shutting off on repeat

I have new plugs/wires/CPS/fuel pump/fuel filter and still kept getting the p0300

took it to my tuner and he said my 02's were acting funny.. so its finally on its last leg.. ordered a new denso 02 and wham problem fixed

It was either that or a vacuum leak.. but i sprayed carb cleaner and no RPM jump..

Hope this helps guys