P2187: System Too Lean at Idle (Bank 1)

P2187 means the engine is running too lean specifically at idle speed on Bank 1. The fuel system is not delivering enough fuel relative to the amount of air entering the engine at low RPM. This is different from P0171, which indicates a lean condition across all operating ranges.

P2187 is a fuel system-related diagnostic trouble code classified as moderate severity. When your vehicle's ECU detects this condition, it stores P2187 and illuminates the check engine light.

If your vehicle has triggered P2187, you may notice one or more of these symptoms:

• Check engine light illuminated
• Rough or unstable idle
• Engine hunting or surging at idle
• Occasional misfires at idle
• Slight hesitation when pulling away from standstill
• Hissing or whistling noise from engine bay at idle

Here are the most common causes of P2187, ranked by how likely they are to be the culprit:

Generally yes, for short-term driving. Short-term driving is acceptable but a lean condition can cause engine overheating and catalyst damage over time. Avoid heavy loads or sustained high-speed driving until diagnosed.

Follow these steps to pinpoint the root cause of P2187:

1. With the engine idling, listen carefully for any hissing or whistling sounds around the intake manifold, vacuum hoses, and PCV system. A vacuum leak is the most common cause and often audible.
2. Use a smoke machine to pressurize the intake system and find vacuum leaks. Smoke will escape from any crack, split hose, or faulty gasket. Pay special attention to the intake manifold gasket and brake servo hose.
3. Check the MAF sensor readings at idle using live data. Compare the actual airflow reading to the manufacturer's specification for your engine. A dirty MAF sensor will underreport airflow, causing the ECU to deliver too little fuel.
4. Monitor short-term and long-term fuel trims at idle. Values above +10% confirm the ECU is adding fuel to compensate for a lean condition. If trims normalise at higher RPM, the leak is only significant at idle vacuum.
5. If no vacuum leak or MAF issue is found, check fuel pressure at idle with a fuel pressure gauge. Low fuel pressure at idle but normal pressure at higher RPM can indicate a failing fuel pressure regulator or weak fuel pump.

Repair costs for P2187 vary depending on the root cause and your vehicle. Here are typical estimates:

P2187 behaves differently depending on your vehicle. Select your car below for model-specific causes, known issues, and adjusted cost estimates:

These codes are often seen alongside P2187 or indicate related issues: