Powertrain, generic (extended)

P2187 System Too Lean at Idle (Bank 1)

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modeNo

P2187 means the long-term fuel trim of bank 1 has to add more fuel than allowed in the idle and low-load range. Many systems, especially Bosch ones, split mixture adaptation into an additive part, which dominates at low airflow, and a multiplicative part for load. An air leak adds a fixed amount of unmeasured air, which matters most at idle, so it shows up in the additive part. GM's 3.6 V6 engines set the code above 7 % (2005) or 6.1 % (2008 LLT, at 520 to 1120 rpm, 1.7 to 7.8 g/s and coolant above 60 °C), and GM's 2024 tables above about 5.5 %, over two trips. On the Opel/GM 2.0 turbo in the Saab 9-5 (2010) the weighted long-term trim must exceed its limit for 4 s continuously or 50 s in total (Type B). Audi traced P2187 with P2279 on 2.0 TFSI engines to a crankcase ventilation valve that let boost into the crankcase; Mazda found A/F sensor wiring on the CX-7 2.3 turbo shorted after brake fluid was spilled on it.

Likely causes

Air leak after the air mass sensor, often at the crankcase ventilation
Damaged front oxygen or A/F sensor wiring
Fuel pressure too low

Symptoms

  • Malfunction indicator lamp on
  • Rough or hunting idle, hissing from the engine bay

Repair estimate

DifficultyMediumDIY possible
Parts and labour€10–400
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

What to check first

  1. Smoke-test the intake
  2. Check PCV system
  3. Watch trims at idle vs cruise

Parts involved

intake manifoldpcv valvevacuum hosemass air flow sensoroxygen sensor upstream

Related codes

P2189P2177P0171P2279P2188

References: gsi.ext.gm.com, gsi.ext.gm.com, saabwisonline.com, static.nhtsa.gov.