English-first OBD-II diagnostics Static, fast, focused lookup pages
CD CheckDTC Garage-grade fault lookup
Open P0300 Try AI Diagnose
Home / Codes / P2187
DTC code page

P2187: System Too Lean at Idle (Bank 1)

Quick answer: Bank 1 is running lean specifically at idle rather than across the full load range.

Drivers also search this fault as system too lean at idle bank 1, bank 1 lean at idle, idle lean bank 1.

Severity: medium Family: powertrain Related paths: 12
Meaning

What P2187 usually means

P2187 is more specific than a general lean code. It says the lean condition shows up at idle, which immediately raises vacuum leaks, PCV faults, intake gasket issues, and idle-air behavior higher than fuel-delivery problems that usually show more under load. That idle-only context is what makes the code valuable: it points you toward unmetered air and low-load mixture problems first.

Fast triage

Start here before chasing parts

  • Scan first: save freeze-frame and pending codes before clearing anything.
  • Confirm the complaint: compare the stored code with current drivability symptoms.
  • Use context: trims, live data, and related codes usually narrow the fault faster than guesswork.
  • Work simplest to hardest: leaks, connectors, maintenance items, and known patterns before expensive components.
Initial checks

What to check first

  • Compare fuel trim at idle versus 2500 RPM because that split is the fastest clue for idle-only lean faults.
  • Inspect PCV lines, intake boots, manifold gasket areas, and brake-booster plumbing before replacing sensors.
  • Listen for hissing and check whether the idle improves when the leak path changes or warms up.
Driving risk

Can you keep driving?

P2187 is often driveable short-term, but repeated stalling, rough idle, or hard starts should move it up in priority quickly.

Moderate urgency: This code often allows short-term driving, but the right fix usually comes faster when you diagnose it early instead of waiting for more codes.
Likely causes

Common causes behind this code

  • Vacuum leak affecting Bank 1 most strongly at idle
  • PCV hose or valve leak adding unmetered air
  • Bank 1 intake-manifold or runner sealing problem
  • Dirty throttle body or idle-air behavior causing unstable low-load airflow
  • MAF bias that looks worst at idle

Cause phrases often tied to this code: vacuum leak, PCV leak, intake manifold gasket, unmetered air at idle, dirty throttle body.

Diagnostic order

Suggested workflow

  1. Review short-term and long-term trim at idle and again off idle.
  2. Inspect for vacuum leaks, PCV faults, and manifold sealing issues on Bank 1.
  3. Check throttle-body condition and airflow plausibility if no leak is obvious.
  4. Rule out exhaust leaks near the upstream sensor if the data story does not fit intake air.
  5. After repair, confirm the idle trim settles and the lean complaint does not return in stop-and-go driving.
Avoid guesswork

Common mistakes

  • Treating P2187 like a generic fuel-pump problem when the code specifically says idle.
  • Replacing the oxygen sensor before checking for unmetered air.
  • Ignoring PCV and intake-gasket leaks because the car drives better once RPM rises.
Repair path

Practical fix guidance

  • Fix the unmetered-air or idle-air problem first, then confirm Bank 1 trim is normal at idle and cruise.
  • If the code remains after leak repair, compare MAF and O2 behavior before ordering more parts.
  • Retest after a full warm-up and a few stoplight idle periods.
Vehicle context

Affected brands in this MVP

Brand hubs help broaden internal linking now and can evolve into make-specific diagnostic notes later.

Aliases and common searches

English phrases tied to P2187

Useful when the driver knows the wording but not the exact DTC yet.

  • system too lean at idle bank 1
  • bank 1 lean at idle
  • idle lean bank 1
Related search intent

Queries this page can answer naturally

  • P2187 code meaning
  • what does P2187 mean
  • lean at idle bank 1
  • P2187 vs P0171
FAQ

Quick questions about P2187

How is P2187 different from P0171?

P2187 says the lean condition is strongest at idle, which usually points toward vacuum leaks or low-load airflow issues faster than a global lean code does.

Can a bad PCV valve cause P2187?

Yes. A leaking PCV path can add unmetered air and create an idle-heavy lean condition.

Why does the car sometimes run better off idle?

Because many vacuum leaks have their strongest effect at idle, then become proportionally smaller as airflow increases.