P0171 Moderate Powertrain

System Too Lean (Bank 1)

Common Causes

Vacuum leak in intake manifold or hoses
Dirty or failed mass airflow sensor
Weak fuel pump or clogged fuel filter
Faulty upstream O2 sensor
Failed PCV valve or hose

Common Symptoms

Rough Idle Engine Stalling Engine Hesitation on Acceleration Engine Misfires Engine Surging at Idle Poor Fuel Economy

Common Repairs

#1 Clean or Replace Mass Airflow Sensor
15–30 min $8 – $120 Very Easy

A dirty MAF sensor sends inaccurate air readings, causing the ECU to run a rich or lean mixture causing rough idle.

Parts Needed

Mass Airflow Sensor (optional)
#2 Clean Throttle Body
20–30 min $5 – $15 Very Easy

Carbon buildup on the throttle plate disrupts airflow at idle. Cleaning often resolves rough idle without parts.

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Quick Info

Code P0171
System Powertrain
Severity Moderate
Repairs 2 known

Disclaimer

This information is for diagnostic guidance only. Always verify repairs with a qualified technician before performing safety-critical work.

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