OBD codes / P2187
P2187
ModerateSystem Too Lean at Idle (Bank 1)
Generally safe to drive — the lean condition lives mostly at idle, and the main day-to-day risk is an inconvenient stall at a light. Still worth fixing promptly: vacuum leaks tend to grow, and the same leak that upsets idle today can set broader lean codes like P0171 later. Diagnose before buying parts; the spread runs from a five-dollar hose to an intake gasket job.
What this code means
P2187 is a more specific cousin of P0171: the mixture on bank 1 goes too lean specifically at idle, even if it is fine at cruising speed. That timing is a diagnostic clue in itself. At idle the engine ingests very little air, so a small vacuum leak that would be a rounding error at highway speed becomes a large share of total airflow — which is why idle-only lean codes point so strongly at unmetered air: cracked or disconnected vacuum hoses, a stuck or leaking PCV valve or hose, intake manifold gasket leaks, a leaking brake booster or its hose, and leaks around the throttle body or intake boots. A MAF sensor misreading at low airflow and marginal fuel delivery can also contribute. The engine often idles rough or hunts while driving above idle feels normal.
Symptoms you might notice
- Rough, uneven, or hunting idle
- Occasional stalling at stops or when coming off throttle
- Sometimes a hissing sound from the engine bay
- Normal behavior once above idle speed
- Check-engine light
What it costs to fix
Varies by vehicle — get it diagnosed.
The repair cost for this code depends too much on your exact vehicle and the underlying cause to quote a meaningful range. Confirm the cause first so you only pay for the fix you actually need.
Diagnose P2187 for my vehicle →Frequently asked
Why is my car only lean at idle and not at speed?
Because a vacuum leak is a fixed-size hole. At idle, when the engine breathes least, that hole supplies a big fraction of the air — too big for the computer to correct. At higher airflow the same leak is proportionally tiny. Idle-only lean behavior is practically the signature of a vacuum leak.
How do mechanics find the leak?
The standard method is a smoke test: low-pressure smoke is fed into the intake and escapes visibly at the leak. Listening for hissing and wiggling hoses at idle can find obvious ones. It beats guessing — intake leaks hide in gaskets, fittings, and the undersides of hoses.
What will fixing P2187 cost?
There is no honest single answer, which is why we do not show a range: a cracked hose or PCV fix can be trivially cheap, while an intake manifold gasket involves real labor, and a MAF or fuel-delivery cause lands in between. The smoke test that pinpoints it is the best money spent.
Is P2187 related to P0171?
Closely — both are bank 1 lean codes. P0171 covers lean across the operating range, while P2187 narrows it to idle. It is common to see them together, and an idle-dominant vacuum leak that worsens can graduate from P2187 to setting both.
Seeing P2187 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P2187 for my vehicleRelated trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P2187 from your phone — see our honest guide to the best OBD2 Bluetooth adapters.
Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.