2006 Jaguar X-type Bank 1 System Too Lean

Hi everyone,
I bought a 2006 Jaguar X-type a month ago. On the first day of
purchasing, the engine light was on. I went to a local Firestone and had
my car repaired. The engine code was P0171, which was Bank 1 System
Too Lean. Firestone replaced a brake booster hose, a vacuum hose, and
an intake valve for me. Then after one day, the code came again. I went
to a small auto repair shop and had my car checked there. The mechanics
there checked my car and replaced an air mass sensor. After three days,
the P0171 code was on again. I went to Jaguar dealership and let them
check my car. They told me that the lower intake had severe air leak. Then
I went to the repair shop and let them repair the lower intake. They
replaced all of the lower and upper intake gaskets and said that there
would not be any leak. Now the engine light is on again. I don't know who
I can trust now. I called the dealer, and he broke the warranty and refused  
reimbursement. I am depressed and helpless now. I am a car virgin. It is
my first car. I don't know what I can do now.