Subaru foreseter - petrol coming out unlit in bursts out exhaust. Ideas on what could cause it?

I’ve got a subaru foreseter ’02 2.5L that I push kind of hard off road on New Zealand beaches.

I had a near dead battery recently so bought a new one but on replacing it I must have wiped the ECU because it has no clue how to run the engine now.

It runs (just) but is super rich, a strong smell of unburnt petrol and is in a constant state of almost stalling. If I blip the accelerator it will either kill the engine or possibly backfire/misfire.

Watch the video, it’s some pretty strange stuff
https://www.youtube.com/watch?v=PooAiOYusFE

Here’s what I know is wrong with it:

• o2 sensor broken ( I believe it’s rear but haven’t confirmed )

And what I have tried:

• Tried doing another ECU reset, slightly better results but still same issues
• Replaced the MAP sensor with another used one (hitachi boost sensor ps60-01) , no difference
• Listened/felt for vacuum leaks, didn’t do a rigorous job by any means but couldn’t find anything obvious

Anyone seen anything like this and have ideas on what to do next?