Lean Codes P0171 & P0174 on my E39 530i

I recently purchased a E39 530i and had an emissions check done. P0174 was listed on the emission sheet but the check engine light was not on. I was able pass and register for the year.

A week later, I was pulling away from a stop at an uphill intersection and the service engine light came on. Codes P0171 and P0174 (Lean bank 1 and bank 2) showed up on my ODBII scanner. Luckily I just passed emissions so I have a year to resolve the issue. 

I have completed these steps to resolve the code, but they still show up. 

• Clean MAF sensor

• Replace engine air filter

• Replace oil filler cap

• DISA valve from previous owner is brand new

• Clean idle control valve

• Clean throttle body 

• Replaced small vacuum hose attached to F-elbow on upper intake boot. It was super brittle and snapped into many pieces when I gently pulled the hose. 
• F-Elbow Part # 13327503677

• Inspected all the other vacuum hoses and I can't see any cracks or brittleness. 

What I have planned:

• Replace fuel filter 

• Replace upper intake boot. Part # 13547505838
• I found a small crack in one of the areas that bend and meet the lower intake boot. You can barely see it and I didn't even noticed it until the third time I took of the boot. This is most likely the culprit and I hope this will clear the code. 

• Replace Vanos oil line. There is oil leaking from the banjo bolt near the thermostat. I don't know if this contributes to the P0174 code.  

• Replace valve cover gaskets. Could a brittle valve cover gasket result in mixture too lean? 

• CCV: I started the 530i and removed the oil filler cap. No strange noises and there was good suction so I don't think the CCV is to blame. 

I believe the previous owner encountered this code and brought it to the dealer to have it fixed. The DISA valve and many vacuum hoses are new, and the MAF sensor was very clean and didn't have grime anywhere. None of the attempted fixes cleared the code so the owner probably got fed up (along with the other issues) and sold the 530i.

Update #1: I changed the upper intake boot  and I haven't seen the service engine light come on. I am hoping the light was intermittently showing up because of the crack in the intake boot and brittle small hose on the F-elbow.

The difference between the new and old intake boot is astonishing. The rubber on the intake boot is so soft and pliable whereas the original is hard as rock. I had some difficulty removing the F-elbow and small air box at the bottom of the boot because of the rubber aging.

Update #2: I haven't had the lean codes show a month and a half later. The culprit is the upper intake boot crack and the small hose on the F-connector. I went ahead and changed the fuel filter since it has never been changed.

Installed new small hose on F Connector

Leave a comment if you have encountered and resolved the codes on your E39. Any help is appreciated.