P2187: System Too Lean at Idle Bank 1
A generic powertrain (engine and transmission) trouble code, same meaning on every brand.
Yes - expect a rough or stalling idle until the leak is found.
Symptoms
- Rough or hunting idle
- Stalling at stops
- Idle problems that disappear once moving
Likely causes, most common first
- Vacuum leak - intake gasket, brake booster hose, PCV system
- Purge valve leaking vapour at idle
- Dirty or leaking throttle body
- Weak fuel delivery at low load
Read P2187 yourself before paying for diagnosis
A basic Bluetooth OBD-II scanner ($20-40) plugs into the port under the dashboard and shows this code with live sensor data on your phone - useful both for confirming the fix and for talking to a shop from an informed position.
What is going on and how it gets diagnosed
P2187 says bank 1 runs lean specifically at idle, and that qualifier is the whole diagnosis. A leak of fixed size matters enormously when the engine is drawing very little air and hardly at all when the throttle is open, which is why the fault appears at every stop light and vanishes on the move.
That pattern narrows the search to unmetered air entering after the air flow sensor: intake gaskets, the brake booster hose, the PCV system, or a purge valve that leaks. A smoke test finds all of them, and it is worth doing before any sensor is replaced - lean codes lead to a great many needlessly replaced oxygen sensors.
Repair options and cost
Typical US independent-shop ranges, parts and labor. Dealers run higher; regional labor rates vary.
Owner reports mentioning P2187
“My Honda Accord Sport has only 47,500 miles and it needs a new Fuel Rail. Code P2187. I have had Hondas for over 20 years and this has never happened before. I read that some 2018 honda model had extended warranty for Fuel Injectors. The Honda Accord should fall under that extended warranty.”2018 Honda Accord · May 2022
Cars that report P2187 most often
Based on mentions of this code in NHTSA owner complaints.
Frequently asked questions
Can I drive with P2187?
Yes - expect a rough or stalling idle until the leak is found.
How much does it cost to fix P2187?
Typical US repair costs range from $60 for the simplest fix (vacuum leak repair) to $700 in the worst case. The right number depends on which cause your car has - see the causes list.
Related codes
The codes closest to P2187. They often appear together, and telling them apart is usually what narrows the diagnosis.
Definition per SAE J2012 standard nomenclature. Symptoms, causes and costs are editorial guidance - always confirm with a diagnosis of your specific vehicle.