P2187: System Too Lean at Idle (Bank 1)
The engine is running lean on bank 1 mainly at idle, so the computer is adding a lot of extra fuel when the car sits still.
What P2187 means
P2187 is a lean code like P0171, but it is specific to idle. At idle, the engine pulls its strongest vacuum and takes in its smallest amount of air, so even a small vacuum leak adds a large percentage of unmetered air. That is why vacuum leaks are the top cause of P2187, followed by PCV problems, MAF sensor issues and exhaust leaks ahead of the upstream sensor. RepairPal also lists damaged spark plugs, fuel that does not meet requirements, injector and pump problems and software updates among the causes. The computer sees the upstream oxygen sensor reporting lean at idle and pushes fuel trim up until it reaches its limit. Shops compare fuel trims at idle and 2,500 RPM. If trims are high at idle but improve at higher RPM, they go hunting for a vacuum leak with a smoke machine. KBB notes the problem often has few driving symptoms but can harm the engine over time.
Common symptoms
- Check engine light on
- Rough or unstable idle
- Hesitation from a stop
- Increased fuel consumption
- Often no other symptoms
Most common causes
- Vacuum leak, the most common cause of a lean idle
- Cracked PCV valve or hose
- Dirty or faulty MAF sensor
- Exhaust leak ahead of the upstream sensor
- Weak fuel pump or dirty injectors
- Engine computer software needing an update
What to check yourself first
Listen for a hiss at idle and inspect vacuum hoses and the PCV hose for cracks. Spray the sensor wires in the MAF with MAF cleaner. If fuel trims are high at idle but close to normal at 2,500 RPM, a vacuum leak is very likely.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Smoke test for vacuum or exhaust leaks | $61-$90 | Smoke testing finds vacuum and exhaust leaks that cause lean readings. |
| Replace PCV valve | $124-$173 | A cracked PCV hose or stuck PCV valve is a classic cause of lean idle. |
| Clean the MAF sensor yourself | $15-$20 | About $17 for a can of CRC MAF cleaner. |
| Replace intake manifold gasket | $683-$834 | If the intake manifold gasket is leaking. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P2188 System Too Rich at Idle (Bank 1)
- P0171 System Too Lean (Bank 1)
- P0174 System Too Lean (Bank 2)
- P0507 Idle Air Control System RPM Higher Than Expected
- P0101 Mass or Volume Air Flow "A" Circuit Range/Performance