I understand it is probably misfiring, but what could be causing it and what could I try to do to fix it? For what its worth, the sputtering comes and goes... sometimes it idles fine, sometimes it begins to sputter. It's a 2003 XJ8.

 

From the DTC "possible Causes":
Cylinder compression low
Worn camshaft / broken valve spring(s)
Fuel delivery pressure (low / high)
Fuel injector(s) blocked / leaking
Fuel injector(s) continuously open
Fuel contamination
Fuel injector circuit fault(s) (Injector DTCs also flagged)
Spark plug failure / fouled / incorrect gap
ECM to ignition module primary circuit fault (Cylinder misfire detected DTC also flagged)
Ignition module ground circuit: open circuit, high resistance
Ignition module / coil failure

Using Occam's Razor, I suspect you will find a failing coil or a split coil boot on cylinder #2. Look at the coil and the spark plug, then if you do not see anything obvious, swap this coil with another one, reset the codes and see what happens.

 

Please tell me where you got a code reader for my/your 2003 XJ8?

 

https://www.jaguarforums.com/forum/g...-%2A%2A-33347/

 

Good stuff. Do you know how to Identify cylinder 2? Also, part no for a replacement coil?

 

What I meant by "swap the coil" is to swap it with another one in the car and see it the code follows the coil or stays with the same cylinder. Cylinder 2 is second from the front, right hand side (Right hand when sitting in the driver seat)

 

All this info is in the free download - JTIS / workshop manual - well worth getting!