P2187
System Too Lean at Idle Bank 1
The engine is getting too much air or not enough fuel when it is idling. This usually causes rough idle, stalling, or a check engine light.
- SEV
- 3/5
- DRIVE
- CAUTION
- DIY
- $20–$200
- SHOP
- $150–$600
Quick answer
AI-CITATION READYWhat it means
Can you drive with it?
Most common causes
- Vacuum leak on bank 1 or after the mass airflow sensor, including cracked hoses, intake duct leaks, or leaking intake manifold gasket
- Stuck open or leaking PCV valve or damaged PCV hose
- EVAP purge valve stuck open, allowing fuel vapor or unmetered air at idle
Typical repair cost
DIY usually runs $20–$200. Typical shop repair lands around $150–$600, depending on the root cause.
01 / Definition
P2187 means the PCM has detected a lean air-fuel condition at idle on bank 1. The fuel trim correction at idle is beyond the allowed limit, usually because of unmetered air, fuel delivery issues, or a sensor problem. Because it occurs mainly at idle, the cause is often a vacuum leak or purge/PCV issue rather than a major fueling fault.
02 / Drive status
With caution. You may be able to drive short distances, but the engine can stall or run poorly at stops. Do not continue driving if the idle gets rough, the engine dies, or the vehicle hesitates badly.
03 / Symptoms
- Check engine light
- Rough idle
- Stalling at idle or when stopping
- Hard starting
- Idle speed that hunts or fluctuates
- Hesitation on acceleration
- Poor fuel economy
- Possible lean misfire codes
04 / Causes
| 1 | Vacuum leak on bank 1 or after the mass airflow sensor, including cracked hoses, intake duct leaks, or leaking intake manifold gasket | high |
|---|---|---|
| 2 | Stuck open or leaking PCV valve or damaged PCV hose | high |
| 3 | EVAP purge valve stuck open, allowing fuel vapor or unmetered air at idle | medium |
| 4 | Dirty, faulty, or contaminated mass airflow sensor | medium |
| 5 | Fuel delivery problem such as low fuel pressure, weak pump, restricted filter, or failing injector on bank 1 | medium |
| 6 | Exhaust leak near the upstream oxygen sensor causing false lean readings | low |
| 7 | Faulty upstream oxygen sensor or wiring issue | low |
05 / Diagnostic sequence
- 01Check for additional codes, especially fuel trim, misfire, MAF, EVAP, and oxygen sensor codes.
- 02Look at live data for short-term and long-term fuel trims at idle and at higher RPM. If trims improve off idle, a vacuum leak is likely.
- 03Inspect the intake system for cracked hoses, loose clamps, broken ducts, and intake manifold gasket leaks.
- 04Check the PCV valve and PCV hoses for sticking, cracks, or disconnection.
- 05Test the EVAP purge valve to make sure it is closed at idle when commanded off.
- 06Clean the MAF sensor only with proper MAF cleaner and verify its readings are reasonable.
- 07Check fuel pressure and fuel delivery if no vacuum or air leak is found.
- 08Inspect upstream oxygen sensor readings and wiring if the problem is still not found.
06 / Repairs
| 1 | Repair vacuum leaks, replace cracked hoses, or replace leaking intake gaskets | $20–$400 |
|---|---|---|
| 2 | Replace a faulty PCV valve or damaged PCV hose | $15–$120 |
| 3 | Replace a stuck open EVAP purge valve | $60–$250 |
| 4 | Clean or replace the mass airflow sensor if readings are incorrect | $15–$300 |
| 5 | Repair fuel delivery issues such as a weak pump, clogged filter, or failing injector | $100–$900 |
| 6 | Replace a faulty upstream oxygen sensor or repair its wiring | $80–$350 |
07 / Related codes
08 / FAQ
Is P2187 the same as a vacuum leak?
Not always, but a vacuum leak is one of the most common causes. The code means the engine is too lean at idle, and a vacuum leak often creates that condition.
Can a bad gas cap cause P2187?
Usually no. A gas cap problem more often causes EVAP codes, not a lean-at-idle code.
Will cleaning the throttle body fix P2187?
Sometimes it helps with idle quality, but it usually does not fix the main cause unless the throttle body is causing an airflow or idle control issue.
Why does the code happen mostly at idle?
At idle, even a small amount of unmetered air has a bigger effect on the fuel mixture. That is why leaks and purge valve problems often show up mainly at idle.
09 / Source and method
- DATA BASIS
- OBD-II REFERENCE + OBD2.HELP
- METHOD
- STATIC VALIDATION
- SAFETY
- INFORMATIONAL
This page combines OBD-II diagnostic reference data with OBD2.help generated diagnostic guidance for code meaning, likely causes, and repair direction.
Publishing uses deterministic schema and build validation, plus manual spot checks on representative pages before release.
Safety-critical diagnosis and repairs should be confirmed with a qualified mechanic, especially when the vehicle is misfiring, overheating, or losing power.