I've done some searching on the forums and have only found one thread about a P0171 code.

It looks like it could be a leak at the brake booster gasket/seal, but I didn't find any clear diagrams or instructions on what to check or what P/Ns to order for the gasket.

Can anyone post more info on this code and any associated diagrams or P/Ns (or where I can get this info)?

 

There's supposed to be a fault with an air seal underneath the intercoolers, might be the same thing. Anyway, reports are it is expensive to repair, ie time consuming.

 

Thanks jagular. The only other lead I have is from an old thread where Brutal was talking about this type of issue on supercharged XFs. He said: "leak is down at the brake booster pipe seal where it goes into the intake elbow below the throttle body. Its right downstream from the EGR (hot exhaust gas) and with alittle time hardens the oring and is a nice big air leak".

Then later "the seal that leaks is on the brake booster pipe where it goes into the supercharger air inlet... a deteriorated rubber o ring inside the air inlet tube and very hard to replace the inlet"

Anywhere I can get an XF service manual or service diagram? I'd love to visually see where this might be and do some test sprays with carb cleaner.

 

I bought a WSM on CD from ebay UK. Also, searching for air leaks try spraying start gas at various locations. You should get an accelleration from idle speed if you hit the spot.