I have been chasing an intermittent P0101 on my XKR. I took it to my Indy who replaced my air filters with Jaguar filters and it went away for a while. It came back last week in the middle of a 300 mile road trip. I checked the air filters (they were fine) and tightened all the clamps on the intake piping (some were loose). I did the return 300 mile trip and no CEL - success!
Except it came back on Sunday after 10 minutes on the interstate.

Always up for a challenge, I hooked up my smoke machine and started looking for leaks. It didn't take long to find it - it was coming out the base of the oil filler tube.
Jaguar will sell you a new tube with an o-ring attached for the very reasonable price of $25. But I thought I could do better. After measuring the old o-ring with my calipers I went to McMasterCarr.com and started hunting for o-rings that are 37mm OD, 27mm ID, and 5mm thick. 1295N629 is a Viton o-ring that is just over $6 for a two-pack and is the perfect size for this application. The old one is on the left and the new one is on the right.

I'll smoke test it tonight and see where else I may be leaking.

 

I just ran a smoke test and no leaks!
Next step is to replace all the couplers on the air tubes - from the air filter to the ram's horn - with silicone couplers and better hose clamps.

 

Nice! I did the same thing and found it in the same spot!

 

Wow, great write up! Thanks. I had no idea about this possible issue.

 

Wrapped this up today. As is well-documented in this board, you can't buy the coupler between the throttle body and T-shaped air intake, but Jaguar is happy to sell you a whole new T-piece + coupler for an unreasonable $800. You can buy and trim a 3.75" to 3.25" silicone reducer and likely not have to worry about that piece ever again.

I was unable to find the rubber couplers between the air tubes - presumably Jaguar will sell you a new tube + coupler but I had already given up the hunt at this point. 2.75" silicone couplers are available and work well. I had bought some nice hose clamps but they were too wide so I just used some still-nice-but-not-as-nice clamps that I already had. Yes, I am a McMaster-Carr junkie. It's nice having a warehouse 8 miles away.





I took it for two test drives and no CEL's were set or pending and the long-term fuel trims looked good. I'll take it out on the highway this weekend and see what happens.

Thanks to gkubrak for documenting the silicone reducer trick.