P2187

System Too Lean at Idle Bank 1

Fuel & air metering Generic OBD-II High

What it means

P2187 means the air-fuel mixture on bank 1 is running too lean specifically at idle — too much air or too little fuel. Because it shows up at idle and clears off-idle, an unmetered vacuum leak is the usual culprit. Expect a rough idle and possible stalling at stops until the leak or airflow fault is corrected.

High

Can I keep driving? Usually yes, but poorly — a lean idle can cause rough running, hesitation, and stalling at stops; some cars drop into limp mode, so get it diagnosed.

Real-world scan data

Seen in

433

scans in the past year

Found in

0.1%

of scans

0.1%

of scans that found faults

Appears alongside · share of P2187 scans

P0300in 22.9% of scans

P2189in 20.3% of scans

P0420in 15.0% of scans

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

Common symptoms

What you'll notice

Check-engine light on
Rough or unstable idle
Hesitation or occasional stalling at idle or low speed
Reduced power / limp mode on some vehicles

Common causes

Most likely first

Unmetered air (vacuum) leak — cracked intake hose, gasket, or a bad PCV connection; the most common causeLikely
Dirty or faulty mass air flow (MAF) sensor under-reading airflowCommon
Low fuel pressure or weak/dirty fuel injectorsCommon
Exhaust leak upstream of the O2 sensor pulling in extra oxygenLess often
Faulty upstream oxygen sensor reporting leanLess often

How to diagnose & fix

Work through it in order

Read freeze-frame and fuel-trim data; a high positive trim at idle that improves off-idle points to a vacuum leak.
Smoke-test or inspect the intake, gaskets, and PCV hoses for unmetered air leaks and fix any found.
Clean or test the MAF sensor and check for the correct airflow reading.
Verify fuel pressure and injector delivery; check for upstream exhaust leaks near the O2 sensor.
Clear the code and confirm fuel trims return to normal at idle.

FAQ

Quick answers

Is it safe to drive with P2187?+

Usually you can drive, but a lean idle can make the engine stall at stops and run rough. Some vehicles limit power. Fix it promptly rather than living with it.

Can I just clear P2187?+

It returns quickly because the ECM keeps measuring a lean mixture. Find the vacuum leak or airflow fault first — that's what resets the trims.

Read & clear P2187 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX