How to fix this code P -0171 power train system too lean (bank 1)

My 2001 DB 4x4 has this code..
what is this ?
thank,s

 

A smoke test is a good start to help you find some leaks. If you have an OBD scanning tool, you can run some diagnostics tests to see which vacuum component is leaking/malfunctioning. Generally this indicates a vacuum leak, but it may also come from a dirty MAF sensor or malfunctioning O2 sensor.

Here's a list of parts to check in order:

O2 sensor - Check if the resistance is within spec
MAF - give it a good cleaning with MAF sensor spray - don't touch the sensor electrode
VSV - apply voltage and see if it opens/closes
PCV
Gas Cap
Fuel pressure regulator
Charcoal Canister
Vac Lines - upgrade to silicon lines with the same inner diameter
Fuel Tank (If it's rusty, there might be pinholes)

follow this video - not the same codes but the same system
https://www.youtube.com/watch?v=nxP4CuzV2EY

 

https://adventuretaco.com/chasing-the-p0171-engine-light/

 

Most likely a vacuum leak

Could be a bad/dirty MAF sensor, 02 or A/F sensor