System Too Rich at Idle (Bank 1)

What it means

The engine computer has found that bank 1 runs rich at idle, and it has cut fuel as far as it can without correcting the mixture. At idle any extra fuel shows up clearly, such as a leaking injector or fuel vapor entering from the EVAP purge system.

Related codes: P2187P2178P0172P0441P2196

Symptoms4

• Check engine light on.
• Unstable idle or shaking at a stop.
• Fuel smell from the exhaust.
• Hard starting after a short stop when the engine is hot.

Possible causes6

• EVAP purge valve stuck open, letting fuel vapor in at idle.
• One or more leaking injectors.
• High fuel pressure from a faulty pressure regulator.
• Mass airflow (MAF) sensor over-reading at low airflow.
• Biased upstream oxygen sensor.
• Faulty coolant temperature sensor.

How to diagnose5

1. Watch the fuel trims; large negative values at idle that improve at higher RPM point to a small extra fuel source such as the purge valve or a leaking injector.
2. Disconnect and temporarily plug the purge valve hose; if the trims improve, the valve is the cause.
3. Measure fuel pressure and check that it holds after shutdown.
4. Compare the MAF reading at idle with the expected value.
5. Compare the coolant temperature sensor reading with the actual temperature.

How to fix5

1. Replace the EVAP purge valve if it is stuck open.
2. Clean or replace the MAF sensor.
3. Replace the coolant temperature sensor or oxygen sensor if proven faulty.
4. Repair the fuel pressure regulator or the leaking injector.
5. Clear the codes and confirm the trims return to normal at idle.

Repair cost

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low for a purge valve or MAF cleaning, and rises when injectors or a pressure regulator are replaced.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions