Gosh, loads of replies, thanks guys,
No signs of smoke at tailpipe.
Disconnected breather with no change also no discernable smoke coming out of it.
Can't remember what injection pulsewidth was at idle, I think it was about 1.8-1.9mS but like an idiot I did not write it down, anyone got data on what it should be?
The misfire was only a minor wobble at idle, not sure if the leads made any difference, but in my opinion was acceptable for an SPi engine.
I only popped the ACR4 on it to check codes and CTS etc. I should have put something else on to check the fuel trims i suppose.
Car does about 3000 miles a year, was serviced last week, has had no other repairs to the engine recently as far as I know.
I was a bit doubtful about my diagnosis, in my opinion most cats don't die of natural causes, they get killed by something, I just could not find a something.
Had a really busy day on Monday and did not want to make a meal of this one.
Shaun