Be sure to identify if you need a 2 or 4 pin coils.

 

Thank you all for the great details and suggestions. I'm looking at codes 0300, 0305, 0306, 1316 and 1000 right now.
I've replaced all the spark plugs and all the coils. A mechanic said the Delphi coils I got replaced them with might be the problem, so I replaced cylinders 2,3,5,6 with genuine Jaguar coils. Still getting a CEL for 1316 and 0300, and now 0305 and 0306.
I've repaced the Air Intake tube (the bellows had a leak) the MAFS, the Throttle obdy and gasket.
Next I'm going to look at and replace the Breather tubes.
The car came with a K&N-type air filter, IN the engine compartment. The Mechanic suggests replacing this with an original Air Intake (from outside the engine). Any thought from the forum on this?
Any suggestions?
I've had this car since August, and I still haven't been able to put a tag on it yet, because it can't pass emissions here in VA.
Grumble grumble...
Thanks for any help you can offer!

 

YA Dave, same codes on my 04 XJ8 but mine are plug 4, 5 and 7... here we go!?!

 

I know I'm late to the party, but this thread has been invaluable. This information PLUS the proper (and expensive) diagnostic tool iCarsoft LR V3.0 saved my biscuits. The one thing I might add that I haven't seen on the forum is that the two cylinders that were misfiring (4 and 8) are at the lowest elevation and both had evidence of water accumulation. The misfires have been fixed and I ran a stunning test drive last night. Now, I'm gonna pull it all apart again and try to find the source of the agua infiltration.