Code P2187: mixture too lean at idle (bank 1)

Original definition (SAE J2012): System Too Lean at Idle Bank 1^[1][2][3][4]

1. 1Air leak in the intake, downstream of the air flow meter: cracked or loose hoses or ducts, intake manifold or throttle body gaskets, brake servo hose or PCV system. This is the most significant cause at idle, because that is when vacuum is at its highest and the leak is proportionally larger.^{[2][3][5][10]}
2. 2Leaking or clogged injectors. Ross-Tech puts them first among the causes of P2187 on VAG cars.^[3][11]
3. 3Exhaust leak upstream of the front lambda sensor, which gives it false readings.^{[2][3][5][11]}
4. 4Dirty or faulty air flow meter (MAF), which measures the incoming air incorrectly.^{[3][5][8][11]}
5. 5Low fuel pressure: weak pump, clogged fuel filter or faulty regulator.^{[2][3][5][11]}
6. 6Faulty PCV valve (crankcase ventilation) or one stuck open, or a stuck-open evaporative emission (EVAP) purge solenoid valve.^{[3][5][8][11]}
7. 7Faulty lambda sensors or other sensors, or a problem in their wiring.^[2][5][8]
8. 8A mechanical engine problem or an ECU fault, which are less common.^[2][5]

• Engine warning light on; with a slightly lean mixture, Mechanic Base says it may be the only thing you notice.^[2][5]Engine warning light: faults that cause it
• Rough or unstable idle, with the revs rising and falling.^[2][5][10]Vibrations: faults that cause it
• The engine may stall.^[2][5]Engine stalls: faults that cause it
• Hesitation when accelerating and misfires.^[2][5]Jerking: faults that cause it
• Difficulty starting the engine.^[2][5]Hard to start: faults that cause it
• Loss of power, when the mixture is very lean.^[5]Less power: faults that cause it
• Hissing or whistling in the engine bay, typical of an air leak.^[2]

1. 1Read all the codes with a diagnostic tool: if there are also lean mixture codes (P0171, P0174), air flow meter codes or misfire codes, deal with them at the same time.^[5]
2. 2Look for air leaks by eye and by ear: cracked or loose hoses, gaskets and hissing in the engine bay. AutoDTCs lists the intake hose, the brake servo hose, the PCV system and the intake manifold and throttle body gaskets as common points.^[2][10]
3. 3Check the fuel trims with the diagnostic tool. If the positive trim is high at idle and drops as the revs go up, it is the typical pattern of a vacuum leak (Ross-Tech, Samarins and AutoDTCs). If it stays the same or gets worse as the revs go up, AutoDTCs points to fuel pressure or flow; and when it is almost zero at idle but rises at higher revs, Samarins points to the air flow meter or fuel pressure.^{[7][8][10][12]}
4. 4To locate the leak, AutoDTCs describes the smoke test (injecting light smoke into the intake at low pressure) as the most reliable method.^[10]
5. 5Check the PCV valve and the evaporative emission (EVAP) purge solenoid valve, which can get stuck open.^{[3][5][8][11]}
6. 6Check the air flow meter, which can be cleaned if it is dirty, and compare its reading with the expected one.^{[3][5][8][11]}
7. 7Measure the fuel pressure and check the injectors.^{[3][5][8][11]}
8. 8Check the exhaust between the engine and the front lambda sensor for leaks.^[5][11]
9. 9Check the lambda sensor only once everything above is in order: it is not usually the first suspect.^[5]

• Injector

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• Fuel pump

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