P2187: System Too Lean at Idle Bank 1
The P2187 code indicates that the engine control module (ECM) has detected a lean air-fuel mixture (too much air or not enough fuel) specifically at idle on Bank 1. This condition can be caused by vacuum leaks, faulty fuel injectors, a weak fuel pump, a clogged fuel filter, or a malfunctioning mass airflow (MAF) sensor. The ECM adjusts fuel trim to compensate, but when the correction exceeds a threshold, the code is set.
01. Most Common Causes
- Vacuum leak (intake manifold gasket, PCV hose, brake booster)
- Faulty mass airflow (MAF) sensor
- Clogged fuel injector(s)
- Weak fuel pump or clogged fuel filter
- Exhaust leak before oxygen sensor
02. Symptoms You Will Notice
- Rough idle or engine hesitation
- Check Engine Light illuminated
- Poor fuel economy
- Engine stalling at idle
- Possible misfire codes
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Inspect for vacuum leaks using a smoke machine or propane enrichment.
Step 3: Check fuel pressure and volume; test fuel pump and filter.
Step 4: Clean or test MAF sensor; compare readings to specifications.
Step 5: Inspect fuel injectors for clogging or leakage; perform balance test.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as a lean condition can cause engine damage, including overheating or detonation. Short trips to a repair shop are acceptable.
How much does it cost to fix?▼
The cost varies depending on the cause. A simple vacuum leak repair may cost $50-$150, while replacing a MAF sensor or fuel pump can range from $200-$600.