Cat light / misfire on cylinder 8 problem.

[jools_s8]

Hi.

Hit a problem with my S8 and I have done some basic fault finding to try and solve the problem.
The car had been running fine, with no indication of any problems. Then came to start it up warm and the CAT light came on. The car is running lumpy and does not want to rev, as you might expect.

I scanned it with VCDS and it came back with these faults:

17604 - Oxygen (Lambda) Sensor Heater Circuit: B1 S1
P1196 - 35-00 - Electrical Malfunction
16518 - Oxygen (Lambda) Sensor B1 S1
P0134 - 35-10 - No Activity - Intermittent
17616 - Fuel Injector for Cylinder 8 (N86)
P1208 - 35-00 - Electrical Malfunction
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 35-00 -
16692 - Cylinder 8
P0308 - 35-00 - Misfire Detected

The Lambda errors have been there since I got it and to date, not caused any issue.
To try and diagnosed or fix the problem, I swapped a coil pack from cyl 8 for cyl 5. I inspected the plugs and could not see anything to cause concern (dark golden brown in colour, electrode not damaged). Not sure when they were changed last, so ordered another set anyway.
After the swap, the same errors were returned, so clear the codes again, let it cool and swapped spark plug 8 for spark plug 5 and swapped the coil packs back to their original cylinders.
It then ran fine, so took it for a spin around the block. No problem, no fault codes and the Lambda errors did not return (presumably as the engine was warm). However as soon as I turned it off then on again, the CAT light reappeared and the fault codes returned.
I supplied the codes to my local Audi specialist, who have ordered another injector, but can't look at it until next Wednesday. However it's VOR back order so is likely to take 7-10 days.
I am posting this up in the hope someone has seen this before and can advise. Would a completely knackered CAT give these errors? I guess a second hand injector is out of the question as it will need a new seal, which is likely to be just as long on order.

Thanks