Ok, bit more info, popped home at lunchtime and disconnected the maf, that made it 100x worse. Car wouldn't idle, tried to sort itself out a couple of times then died, reconnected and it idled perfectly. Decided to clean it out and that has really made no difference. took it for a quick blast and noticed that as i got to about 4-4.500 rpm the power would totally disappear and the cat would wake a dreadful rattle. Really does seem like that cat to me. Am still going to plug the diagnostic machine in after work to check out if anything else is happening though.