System Too Lean at Idle (Bank 1)
What does P2187 mean?
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.
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
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.
Frequently 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.