I just wanted to share my recent experience of a "Restricted Performance" problem on my XK8 (2000).
The problem would start when the car reached its normal running temperature. The Restricted Performance message would pop up and I could feel the engine running rough. The speed limiter also kicked in at that point meaning going faster than 80km/hr and I was getting shaken to bits. Curiously though, after about 15 minutes the rough running and the message would disappear and all was well again.
I got a Jag OBD2 reader from iCarsoft - which does work and out popped the following error codes:
P0301 Cylinder 1 misfire
P0351 Ignition coil A primary/secondary circuit
P1316 Injector driver misfire
P0333 Knock sensor 2 circuit high input (bank 2)
P1313 Misfire rate catalyst damage bank 1
B0333 Unknown code
I ended up taking the car to Mike Roddy Jaguar - Moorabbin, Victoria Australia - and they replaced the air filter, all the plugs and one coil. Since then it's all been smooth running.
If you are ever in that part of Australia do check out Mike Roddy's garage. They service Jaguars but also restore them. I had a look round their latest E-Type project and it was fantastic. I think they are putting it up for sale sometime in the future.

 

P1316 has a different meaning I believe - like P1313 but bank 2. Be wary trusting meanings of codes from that tool.