Dear Forum,
What is the function of the extra plastic 'box' attached (after the MAF) to the pipe between the Air box and the Throttle Body, please?
XJ8 4.2L-V8 Air Cleaner Intake-Duct Hose Tube C2C25837

I believe its a resonator, basically a muffler for intake noise.

Thanks XJ8JR, unfortunately my Syrian 'mechanic' has leaned on it and broken it and attempted to stick it back together with silicone sealant. I now have Restricted Performance arising from both banks running lean and very high LTFT's attempting to annul the resulting vacuum leak!

Yeah that'll definitely cause a bad leak. You could just leave it off and seal up the hole.

Found out in the end the silicone stuck-on resonator was not the problem. I had fitted an Oil Catch Can which my 'mechanic' did not like; he had removed it and replaced the Part Load Breather pipe? (I can never remember which is which - the one from the PCV Valve to the TB). Unfortunately, the replacement pipe had O Rings that were so brittle they snapped in two as I removed them, and one end had no clip to retain it in position! As a short term measure, I have replaced the O Rings and I have 'cable-tied' the broken retaining clip to the PCV Valve in order to keep it tightly in place!!

The P0171 & P0174 codes have disappeared and my LTFT are both returning from 19.58% to 'normal'.......Boy, these fuel trims are a great way to periodically open your eyes for vacuum leaks!

Are you sure you should still be using this "mechanic" ? Jaguars are not Russian tanks.

Oh to have the agony of choice!

There is one Main Jaguar Dealer here in Dubai and their fees are astronomical for a 13-year old car. Even if you are prepared to pay them, they ship work out to mechanics in Sharjah - The Emirate next door (where rents for premises etc. are so much cheaper) and still charge you their Main Dealer prices!. My 'mechanic' is one of those ex-Jaguar guys; but like all of the Indian, Pakistani, Egyptian and Syrian guys here, they offer cheaper prices because they reuse everything - Gaskets, parts, everything! They have heard of planned maintenance, but they want no truck with it!! If it aint broke, they don't fix it until it is broke.....I do as much as I can myself (with the excellent help of this Forum), but obviously, suspension bushings and timing-chain tensioner blades are a little beyond an amateur mechanic without a hoist etc.
Occasionally, it works out in your favour; for example, I have just had a reconditioned Transmission fitted for £800 all in and Jack the Jaguar (blame the wife) is now shifting as sweetly as a sweet shifting thing........