P2187 — System Too Lean at Idle (Bank 1)
Moderate severityWhat it means
P2187 is stored when the engine control unit sees a fault involving the air–fuel mixture at idle on bank 1. This code is set when the mixture on bank 1 is off specifically at idle, where small air or fuel changes have the biggest effect. “Lean” means the exhaust shows more air (or less fuel) than ideal, and the control unit has run out of room to add fuel to correct it.
Common symptoms
- Hesitation, misfire or rough idle
- Rough or unstable idle
- Stalling at a stop
- Higher fuel consumption
Likely causes
- An intake or vacuum leak letting in unmetered air
- A weak fuel pump, clogged filter/injectors or a dirty MAF sensor
- A vacuum leak (lean) or a stuck purge valve
- A leaking injector or fuel-pressure issue (rich)
What to check first
- Look for intake/vacuum leaks and check fuel pressure
- Watch fuel trims and the MAF reading in live data
- Watch idle fuel trims on bank 1 in live data
- Look for vacuum leaks and check the purge valve
Can you keep driving?
Usually drivable, but stalling at idle is a safety concern — diagnose soon.
Frequently asked questions
What is the most common cause of P2187?
The most likely cause is: An intake or vacuum leak letting in unmetered air. Several other faults can set P2187 as well, so confirm the real cause with live data and the checks above before replacing any parts.
Can I just clear P2187 and keep driving?
Clearing P2187 with an OBD2 scanner turns the warning light off, but if the underlying fault has not been repaired the code will usually come back within a few drive cycles. Fix the cause first, then clear the code to confirm the repair worked.
How serious is P2187?
P2187 is a moderate-severity code. The car is often still drivable, but have it diagnosed soon — the underlying problem can get worse and it may fail an emissions test.
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