if the o2 sensor does nothing or its still bad afterwards check:
coolant temp sensor - the 2wire one, can be replaced with any of the same colour
cam timing - my 32 was a tooth out, didn't realise and wondered my the rb20 was such a pos, the ppl i sold it to worked it out and it goes wicked sick now
also, i think i got about 700 out of a tank once with my turbo brick, but my tank holds about 65 litres
just change the motor for an rb25neo