Just paid for a new brake booster and for installation. 10 minutes later. Check engine light back on. Same damn codes. This time the P0171 says pending. And P0174 is current. What a waste of money !!!! Seems like nobody can fix this damn vacuum leak. What do I do now ????

 

Apart from checking for vac leaks, I assume you...:
...P0171: checked and cleaned the MAF sensor? Checked (replaced?) bank 1 upstream O2 sensor?
...P0174: Checked (replaced?) bank 2 upstream O2 sensor?

And I found this - it's S-Type, but I'd assume there is an equivalent X-Type situation...:

 

https://www.jaguarforums.com/forum/x-type-x400-14/p0171-lean-code-only-214539/

https://www.jaguarforums.com/forum/x-type-x400-14/wont-rev-past-3k-system-too-lean-w-video-257455/

 

Ok. So. New brake booster. Booster vaccum line. Imt o rings. And still need to do the pcv valve and hose. Too cold today. I had the same issue last year. P0174 only. It was finally resolved (I thought). When my mechanic changed out the bank 2 upstream sensor. The one under the air box. I bought an oem Jaguar sensor. For the ridiculous price of $350 bux. That got rid of the check engine light and I was able to get and pass my inspection. 5 months later I got the P0174 code again. Then in the last few months getting P0174. And occasionally P0171. Is it possible that the new sensor crapped out after 5 months ? Then bank 1 sensor also craps out ?? How long are these sensors supposed to last. Can’t get the cat inspected. And my inspection has been expired since October. Don’t know what else to do. I’m reluctantly thinking of taking my car to the dealer !!! Any help
is greatly appreciated. Happy Holidays