P2187 System Too Lean at Idle (Bank 1)

P2187 sets when bank 1 runs lean specifically at idle — the fuel trims add a large positive correction at low load, which usually points to unmetered air entering after the airflow sensor.

Code details

Generic OBD-II · P2

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not chase fuel-system parts before smoke-testing for vacuum leaks, because idle-only lean codes are most often unmetered air.

Symptoms of P2187

Rough or unstable idle, sometimes stalling.
Check-engine light with high idle fuel trims.
Hesitation just off idle.

Common causes of P2187

A vacuum leak, split intake boot, or PCV hose.
A leaking brake booster or its hose.
A dirty or failing MAF sensor.
Low fuel pressure at idle.

Useful checks before replacing parts

Smoke-test the intake for vacuum leaks, PCV and brake-booster hoses.
Inspect the intake boot and throttle-body gaskets for splits.
Check fuel pressure and MAF calibration at idle.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.