P2187: System Too Lean at Idle (Bank 1)
Quick Answer
Safe to drive (short-term)
P2187 means the engine is running too lean specifically at idle speed on Bank 1. The fuel system is not delivering enough fuel relative to the amount of air entering the engine at low RPM. This is different from P0171, which indicates a lean condition across all operating ranges.
- Severity
- Moderate · Fuel System
- Estimated repair cost
- From €35 to €380+, varies by vehicle
€35 or €380, depending on your car.
- MAF sensor cleaning or replacement€35–€240
- Intake manifold gasket replacement€120–€380
A scan shows whether P2187 is really stored on your car, which codes sit next to it and how urgent each one is.
A scan needs a Bluetooth OBD2 adapter (Bluetooth LE on iPhone), about €25-60; the built-in demo runs without one. See which adapter to buy
What does P2187 mean?
P2187 is a fuel system-related diagnostic trouble code classified as moderate severity.
Where it is on the car
- Air filter box
- Mass airflow sensor (MAF)
- Throttle body and throttle position sensor
- Intake manifold and MAP sensor
- Engine (cylinder head)
A lean code usually means extra air is getting in after the MAF sensor, for example through a leaking intake hose, a cracked vacuum line or a worn manifold gasket. The intake manifold side is the first place to look. A dirty MAF sensor that reads too little air is the other common cause.
What are the symptoms of P2187?
- Check engine light illuminated
- Rough or unstable idle
- Engine hunting or surging at idle
- Occasional misfires at idle
- Slight hesitation when pulling away from standstill
- Hissing or whistling noise from engine bay at idle
What causes P2187?
Vacuum leak (cracked hose, intake gasket, PCV valve)
: high
Faulty or dirty mass airflow (MAF) sensor
: high
Leaking fuel injector seal or O-ring
: medium
Weak fuel pump or clogged fuel filter
: medium
Cracked intake manifold
: low
Faulty oxygen sensor providing incorrect feedback
: low
Is it safe to drive with P2187?
Generally yes, for short-term driving. Short-term driving is acceptable but a lean condition can cause engine overheating and catalyst damage over time. Avoid heavy loads or sustained high-speed driving until diagnosed.
How do you diagnose P2187?
- With the engine idling, listen carefully for any hissing or whistling sounds around the intake manifold, vacuum hoses, and PCV system. A vacuum leak is a usual cause and is often audible.
- Use a smoke machine to pressurize the intake system and find vacuum leaks. Smoke will escape from any crack, split hose, or faulty gasket. Pay special attention to the intake manifold gasket and brake servo hose.
- Check the MAF sensor readings at idle using live data. Compare the actual airflow reading to the manufacturer's specification for your engine. A dirty MAF sensor will underreport airflow, causing the ECU to deliver too little fuel.
- Monitor short-term and long-term fuel trims at idle. Values above +10% confirm the ECU is adding fuel to compensate for a lean condition. If trims normalise at higher RPM, the leak is only significant at idle vacuum.
- If no vacuum leak or MAF issue is found, check fuel pressure at idle with a fuel pressure gauge. Low fuel pressure at idle but normal pressure at higher RPM can indicate a failing fuel pressure regulator or weak fuel pump.
How much does P2187 cost to fix?
| Repair | Parts Cost | Labor Cost | Total Estimate | DIY Difficulty |
|---|---|---|---|---|
| Vacuum hose replacement | €5–€30 | €40–€120 | €45–€150 | Easy |
| MAF sensor cleaning or replacement | €15–€180 | €20–€60 | €35–€240 | Easy |
| Intake manifold gasket replacement | €20–€80 | €100–€300 | €120–€380 | Moderate |
| Fuel injector seal replacement | €15–€60 | €80–€200 | €95–€260 | Moderate |
| PCV valve replacement | €20–€100 | €40–€150 | €60–€250 | Easy |
Prices estimated as of October 2026. Costs vary by region, vehicle, and shop.
Full repair guides
P2187 on specific vehicles
Volkswagen
Volkswagen Golf
2005-2024
On the 2.0 TFSI engines BPY, CCTA and CBFA, Ross-Tech points to the crankcase ventilation: on the BPY, a faulty breather valve typically shows as full engine vacuum at the oil filler cap at idle.
Source: wiki.ross-tech.com
P2187 on BMW
BMW 3 Series
Audi
Audi A3
2005-2024
On VAG petrol engines Ross-Tech lists leaking or blocked injectors, an intake air leak after the air mass meter and an exhaust leak as possible causes of P2187.
Source: wiki.ross-tech.com
Opel
Opel Astra
2004-2023
P2187 means the engine control sees more air than fuel at idle on bank 1, so unmetered air after the air mass meter is the first thing to rule out.
Related diagnostic codes
Common questions about P2187
- What does P2187 mean?
- P2187 means your engine is running too lean (too much air relative to fuel) specifically at idle speed on Bank 1. The ECU has detected that it needs to add more fuel than expected to maintain the correct air-fuel ratio at idle.
- What is the difference between P0171 and P2187?
- P0171 indicates a lean condition across all engine operating conditions, while P2187 is lean only at idle. P2187 strongly suggests a vacuum leak, since vacuum leaks have the most effect at idle when airflow is lowest and manifold vacuum is highest.
- Can a vacuum leak cause P2187?
- Yes, a vacuum leak is a usual cause of P2187. At idle, engine vacuum is at its highest, so even a small leak allows significant unmetered air into the intake. A smoke test is the best way to find vacuum leaks.
- Will cleaning the MAF sensor fix P2187?
- It can. A contaminated MAF sensor underreads airflow, causing the ECU to deliver insufficient fuel. Cleaning with dedicated MAF sensor cleaner spray is a simple first step that costs under 10 EUR and takes 10 minutes.
- Is it safe to drive with P2187?
- Short-term driving is safe, but a persistent lean condition at idle causes rough running and can lead to catalytic converter overheating over time. Diagnose and repair the cause within a few weeks.
Read our detailed guides
Sources
- wiki.ross-tech.com wiki.ross-tech.com/wiki/index.php/18619/P2187/008583
- en.wikipedia.org en.wikipedia.org/wiki/BMW_N52
- en.wikipedia.org en.wikipedia.org/wiki/BMW_N55