Ok, heres what I did. I reset the ecu for the pure fun of doing it and I got the everythings fine code (0505). The screw was back to where it was, fully counter clockwise and I went for a short drive. The check engine light came on. So I stopped and checked the engine, and it was still there. (sorry, that was a lame joke.) But seriously the light came on and turned off. It was not in any particular sequence, sometimes it did a flick on and off, sometimes it stayed on for a while. It did seem to be affected by how I stabbed the gas (air) pedel. Sometimes by stabbing the gas, it would come on and by letting it off, it would go out, othertimes it came on by itself and letting off the air pedel it would go out again. The fuel tank was on reserve, but its never ever come on and I have run the car out a few times. Another thing, The wire that goes to the cat has been cut by something or someone. This wire goes to a sensor that is bolted into the back end of the cat. I assume this is a tempreture sensor?
ANyway I got back home and did the code again and it came back with everythings fine (0505). Is there something Im missing or have done wrong?

 

That thing in the back of the cat is an Oxygen sensor...you need to get a new one, or try to fix the wiring.

 

I agree with the advice from Mzmtg. Of course, we are assuming your New Zealand 2.5 liter engine has similar emission controls to the US models.