Fuel & air metering · Powertrain · generic (SAE-defined)
P2187: System Too Lean at Idle (Bank 1)
P2187 means the engine computer detected that bank 1 runs too lean specifically at idle, needing more added fuel than it is allowed to supply.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P2187 sets
The powertrain control module (PCM) calculates a separate adaptive fuel correction for idle. If the bank 1 idle correction reaches its rich-side limit because the upstream oxygen sensor keeps reading lean, P2187 sets. Because unmetered air has the largest effect at idle, vacuum leaks are a leading suspect. Thresholds vary by manufacturer.
Common causes of P2187
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Vacuum leak from a cracked hose or intake gasket
- Faulty positive crankcase ventilation (PCV) valve or hose
- Leaking brake booster hose
- Dirty or faulty mass air flow (MAF) sensor
- Exhaust leak upstream of the bank 1 sensor 1
- Low fuel pressure
P2187 symptoms
- Check engine light on
- Rough or unstable idle
- Hissing sound from the engine bay
- Possible stalling at stops
How P2187 is diagnosed
- Scan for codes and capture freeze frame data.
- Check fuel trims at idle and at 2,500 rpm; improvement at higher speed suggests a vacuum leak.
- Smoke-test the intake, PCV system, and brake booster line.
- Inspect the intake boot and hoses for cracks.
- Verify MAF readings at idle.
- Check fuel pressure if no leak is found.
Typical fixes for P2187
- Repair vacuum hoses or intake gaskets
- Replace the PCV valve or hoses
- Clean or replace the MAF sensor
- Repair exhaust leaks near the upstream sensor
- Address low fuel pressure
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Manufacturer notes
Commonly reported on some Volkswagen and Audi engines, where crankcase ventilation and intake leaks are frequent suspects; check factory service information.
Related codes & warning lights
P2187 FAQ
What does code P2187 mean?
P2187 means the engine computer detected that bank 1 runs too lean specifically at idle, needing more added fuel than it is allowed to supply. The standard definition is "System Too Lean at Idle (Bank 1)."
Can I drive with a P2187 code?
Typically yes in the short term, though the idle may be rough. Get it checked soon, since lean idle conditions often come from vacuum leaks that can worsen.
Is a vacuum leak the most common cause of P2187?
It is a leading suspect because extra air has the biggest impact when airflow is low at idle; a smoke test is the quickest way to confirm.
Can a PCV problem set P2187?
Yes. A torn PCV diaphragm or cracked crankcase vent hose can let unmetered air into the intake.
Keep researching
Engine guides by brand (known issues, specs)
More fuel & air metering codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
- California Air Resources Board — On-Board Diagnostic (OBD) Program
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.