I’ve worked on jaguars for most of my life I can tell you about any of the models up till about 2000 after that I’m in the dark give me an XJS and I could put it together with my eyes closed .
To the point I recently got hold of a 2005 XJ8L I got it really cheap it had blown head gaskets so replaced the head gaskets , timing chains thermostat ,radiator and it ran ok but some thing does not seem right I changed one coil
And the car runs great at idle smooth
until you get it out on the highway now if you just cruise along it runs ok but if you put your foot down it starts pinging and puts up all kinds of codes for example missfires on 1 2 4 5 7 6 8 all except 3 and it goes in to restricted mode I perhaps thought it could be the crank sensor or plugged cats has any body else out there had this same problem could use some advice
Thank you so much Mark

 

I'd check the cats first.