Fuel and air

P2187 — System Too Lean at Idle (Bank 1)

Severity: medium Drive with care, to a shop

What P2187 means

The engine computer watches the oxygen sensor and adjusts fuel delivery with fuel trims. P2187 sets when, at idle on bank 1, the trims have reached their limit adding fuel and the mixture is still lean. This usually means extra air is getting in or too little fuel is being delivered.

Symptoms

  • Rough or unstable idle
  • Stalling at stops or when you lift off the throttle
  • Check Engine light on
  • Often appears with P0171
  • Misfire or shaking
  • Possible higher fuel consumption

Possible causes

  1. Vacuum or intake air leak (cracked hoses, intake gasket, ducts)
  2. PCV system leak
  3. Dirty throttle body
  4. Stuck or faulty idle air control valve (on vehicles that have one)
  5. Dirty or inaccurate MAF sensor
  6. Low fuel pressure (pump, filter, regulator)
  7. Clogged bank 1 injectors
  8. Exhaust leak ahead of the oxygen sensor

How to diagnose

  1. Read codes and freeze frame data and look for related codes such as P0171
  2. Check short and long term fuel trims at idle and at about 2,500 rpm
  3. Inspect intake ducts and vacuum hoses, then smoke test to find air leaks
  4. Check PCV hoses and valve, the oil fill cap and the dipstick seal
  5. Compare MAF readings with expected values and inspect the sensor
  6. Inspect and clean the throttle body and check the idle air control operation
  7. Measure fuel pressure at idle and under load
  8. Check injector circuits and operation, and inspect the exhaust for leaks

Common fixes

  • Repair the air leak: replace the hose, duct or gasket
  • Replace a faulty PCV valve or hose
  • Clean the throttle body and perform an idle relearn
  • Clean or replace the MAF sensor
  • Replace the fuel filter, pump or pressure regulator
  • Clean or replace the injectors

Questions and answers

What does P2187 mean?

It means the mixture is too lean at idle on bank 1. The computer cannot add enough fuel to compensate, usually because of extra air or low fuel delivery.

What is the most common cause of P2187?

Most often it is a vacuum or intake air leak, or a PCV leak. After that, check the throttle body, MAF sensor and fuel pressure.

Can I drive with P2187?

For a short time until it is fixed, yes. The engine may stall, and a lean mixture can eventually harm the catalytic converter, so do not put off diagnosis.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.