P2187
System Too Lean at Idle (Bank 1)
If your vehicle's onboard computer has flagged the diagnostic trouble code P2187, it refers to a detected anomaly regarding "System Too Lean at Idle (Bank 1)". This systemic engine fault needs a targeted check before symptoms expand.
Driver's Summary
Storing code P2187 is your car's way of telling you something is wrong with the system too lean at idle (bank 1). In practice, this fault causes rough idle, stalling at stop signs, engine surging. This is a moderate-severity fault — plan a repair shop visit within the week to keep it from escalating.
Symptoms
Rough idle, stalling at stop signs, engine surging
Common Causes
- Stuck open purge valve
- Vacuum leak
- Failing MAF sensor
- Fuel pump pressure low
How to Fix
- 1 Test EVAP purge valve
- 2 Search for vacuum leaks
- 3 Clean or replace MAF sensor
- 4 Test fuel pressure at idle
Technical Explanation
The ECM detects code P2187 by continuously monitoring the relevant sensor circuit against calibrated threshold values stored in its non-volatile memory. The control module samples the circuit continuously during normal operation, using both voltage level monitoring and frequency analysis to detect open circuits, shorts to ground, shorts to battery voltage, and high-resistance connections. The fault remains stored in memory even after the MIL is cleared; it becomes a confirmed DTC after failing two consecutive drive cycles, and the PCM logs a freeze frame record of the engine's exact operating state at the moment of detection.
Is It Safe to Drive?
While the vehicle is typically drivable with P2187 active, avoid towing, aggressive acceleration, or extended highway driving until the fault is resolved. The primary risk is accelerated wear on stuck open purge valve and vacuum leak.
Mechanic's Pro Tip
The most common mistake with P2187 is replacing the sensor without verifying the reference voltage and ground integrity first. Use a scan tool to monitor the sensor's live output; a truly failed sensor shows a stuck, flatlined reading — a sensor that fluctuates but reads slightly off usually indicates a wiring or vacuum issue, not a dead sensor. Always spray electrical contact cleaner on the connector pins before condemning the sensor.
Purge valve: $150; MAF: $200; Fuel pump: $400 - $600