2001 S type P0171 and P0174 codes
 

Came home and my wife informed me that our 2001 S type had an engine light on and was running rough. Checked codes and P0171 and P0174 came up. Seeing both banks running lean i thought of a vacuum leak. Sure enough upon inspection I heard a hissing sound along the back side of the engine (by cylinder 6) There is a hard plastic line that connects to a rubber elbow and heads down toward the intake valley area. It was "sucked in" and cracked. A mechanic (FRED) at the service garage suggested to use a silicone spark plug boot as a replacement . Worked perfect . Lights stayed off - car ran great - for two months.

Two months later - same codes come on. Did smoke test and smoke came leaking out of intake pan area. Can't see exactly where the leak is cause the intake, fuel rail are in the way. So i removed the intake, fuel rail and found the matching rubber elbow to the one i replaced earlier in the intake pan cover. There is a square metal box with an outlet on it. The defect rubber elbow was imploded and cracked. It is 15 years old but the material was a poor choice for this vacuum application. I will go over to Jaguar tomorrow and order the replacement hose fittings and get that Jaguar feeling. The last time i got the feeling was when i paid $ 7.65 each for the special pop rivets that hold the front brake dust shields on. Little did i know that there were like large pop rivets at Harbor Freight about ten cents each.!!

That elbow is a common failure.

Be sure to also replace the IMT o-rings since you have the inlet manifolds removed.

Given the age of the vehicle, it may also be a good idea to replace the injector seals.

Take care when reassembling the manifolds as the brass inserts in the lower manifold can become loose if too much torque is applied.