System Too Lean at Idle (Bank 1)
The P2187 code means the vehicle's onboard diagnostic system has detected: System Too Lean at Idle (Bank 1). This is a serious severity code.
- Keep driving?
- Limited driving only
- DIY difficulty
- medium
- Estimated cost
- $0-$50 for vacuum hose repair; $0 for cleaning
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Common Symptoms
- Rough idle only (normal at higher RPM)
- Check Engine Light on
- Stalling at idle
Probable Causes (Ranked by Likelihood)
- Small vacuum leak that only affects idle (high RPM masks it) Very High
- Dirty IAC valve or carbon-restricted throttle body idle port High
- Clogged idle air passage Moderate
Common Fixes by Vehicle
What techs usually find when diagnosing P2187 on specific vehicles — tap your vehicle for the fix and the exact part:
2009-2017 VW GTI/Jetta/Audi A4 2.0T TSI moderate DIY
VW 2.0T TSI P2187 is almost always the PCV valve built into the valve cover. The diaphragm tears, creating a huge idle vacuum leak. Replace the entire valve cover assembly (06K 103 469 AC for EA888 Gen3). Smoke test after install to verify all leaks are fixed.
Labor: 2-3 hours2014-2019 Mazda3/6/CX-5 2.0L/2.5L SkyActiv easy DIY
Mazda SkyActiv P2187 points to a vacuum leak from the intake manifold gasket or a torn PCV hose. Smoke test at idle. Common failure: hairline crack at the PCV elbow on top of the valve cover (Mazda). Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.
Labor: 30 min2005-2015 Ford Focus/Fusion 2.0L/2.5L easy DIY
Check the brake booster check valve and hose -- a cracked check valve causes a big idle vacuum leak that only shows at idle (P2187) because at cruise the manifold vacuum drops and masks it. $10 fix with a Dorman or Motorcraft replacement.
Labor: 15 minFrequently Asked Questions
What makes P2187 different from P0171?
P0171 (lean Bank 1) is triggered based on long-term fuel trim across all operating conditions. P2187 is specifically triggered at idle only. This distinction helps narrow the cause to issues that primarily affect idle: small vacuum leaks or restricted idle passages.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
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Monitor STFT (short-term fuel trim) at idle. Large positive values confirm lean condition at idle only.
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Rev the engine to 2,000 RPM and check STFT: if it normalizes at higher RPM, the leak is small and only significant at idle.
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Search for small vacuum leaks using a smoke machine. Small leaks invisible to the eye show up clearly.
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Clean the throttle body idle bypass ports and IAC valve.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- Volkswagen Jetta and Passat (common idle vacuum issues)
- Audi A4 and A6
- BMW 3 and 5 Series
- Subaru Outback and Forester
Related Codes
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