A Code P0171/p0174 lean fuel condition can be caused by:
* Low fuel pressure due to a weak pump or leaky fuel 1. pressure regulator
. (use a fuel pressure gauge to check fuel pressure at idle)
* Dirty fuel injectors. (try cleaning the injectors)
* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body
. (Use a vacuum gauge to check for low intake vacuum)
* Leaky EGR valve. (Check operation of EGR valve)
* Leaky PCV Valve or hose. (Check valve
and hose connections)
* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor
wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)