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.

Severity3/5 Moderate

Can I drive?⚠ 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.

DIY

$20–$200

Shop

$150–$600

Difficulty

intermediate

What It Means

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.

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

Common Causes

1. Vacuum leak on bank 1 or after the mass airflow sensor, including cracked hoses, intake duct leaks, or leaking intake manifold gaskethigh

2. Stuck open or leaking PCV valve or damaged PCV hosehigh

3. EVAP purge valve stuck open, allowing fuel vapor or unmetered air at idlemedium

4. Dirty, faulty, or contaminated mass airflow sensormedium

5. Fuel delivery problem such as low fuel pressure, weak pump, restricted filter, or failing injector on bank 1medium

6. Exhaust leak near the upstream oxygen sensor causing false lean readingslow

7. Faulty upstream oxygen sensor or wiring issuelow

Related Codes

P0171 P0174 P0300 P0101 P0441 P2195

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.