Celica Forums General Discussion Engine and Performance codes p0300 and p0304 HELP

I’m really stuck.

I have the codes p0300 and p0304 on my 2000 gts. I’ve changed spark plugs, tested fuel injectors, tested maf, changed coils, and still nothing.

Some symptoms:
Loss of power
poor mileage
slow startups
rough idle
running rich
black smoke coming out of exhaust
and obviously the misfire.

On my code reader I ran a test for my o2 sensors and it says bank 1 sensor 2 fails. But wouldn’t that come up in my codes?

I appreciate any help I can get as i’m really stuck with this.

and oil in my 4th spark plug well