P0171 OBD CODE

Good job by a guy who said his mechanical skills were limited.

A PO171 code indicates the engine is running lean. This could mean there is too much air and/or not enough fuel. You can capture this problem by using a scan tool and viewing the short and long fuel trimmings.

A lean fuel mix:
Low fuel pressure, dirty fuel injectors, vacuum leaks
Leaky EGR valve meaning its open when not suppose to, dirty or bad MAF sensor.

The MAF sensor is located at the air cleaner, its in between the throttle body and air cleaner. Also with the IAT sensor

Airflow sensors are real common on toyotas. Before you start in that direction though I would make sure there are no air leaks after the airflow sensor. If no leak 99% of the time a p0171 on a yota indicates a bad airflow sensor.

P0171 indicate the engine is running lean. This means there is too much air and/or not enough fuel.

You can confirm the engine is running lean by looking at Short Term Fuel Trim (STFT) and Long Term Fuel Trim (LTFT). Normally, STFT and LTFT should be plus or minus 8 from zero. If STFT and/or LTFT are more than about +10 or higher, it indicates the engine is running LEAN. Negative numbers (-10 or more) indicates the engine is running RICH.

A lean fuel condition can be caused by:

* Low fuel pressure due to a weak pump or leaky fuel 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)