Cheers Andy,

Do you think it could something to do with the MAP sensor? I haven't actually had a chance to check for leaks in the intake manifold that could mess up with the MAP readings, but I know that the ECU sometimes uses a base value for manifold absolute pressure if it doesn't trust the readings or the sensor stops working or something.. but wouldn't this give me an engine warning light or something?

Apart from that, I seriously have no idea why it's failing so bad..

It's definately running rich (checked the plugs - totally black/dry), but if it's not a faulty sensor of some kind causing it, I have no idea what else it might be.

I suppose it can only really be found out with a bit of diagnostic.. just exploring my options really