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.
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.
Related codes
Often seen with P2187
Read & clear P2187 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX