P0505

What it means

P0505 is the generic code for an idle control system fault. The engine control unit compares actual idle speed with its target idle speed and has found it cannot hold it within the expected range, usually because the idle speed is persistently too high, too low or unstable. How idle is controlled (idle air control valve or electronic throttle body) depends on the vehicle and engine.

Symptoms

• Idle speed too high, too low or hunting up and down
• Engine stalls or nearly stalls when coming to a stop
• Rough idle, especially when the engine is warm or under electrical load
• Idle speed drops when the air conditioning or headlights are switched on
• Hesitation or poor response when pulling away
• Engine warning light on

Possible causes

• Unmetered air entering through an intake leak, such as a split hose, loose clamp, worn gasket or leaking brake servo hoselikely
• Dirty or carbon-fouled throttle body or idle air passages restricting airflow at idlelikely
• Faulty or sticking idle air control valve, or a throttle actuator that cannot hold the commanded position (depending on the system fitted)likely
• Faulty crankcase ventilation system or purge valve stuck open, letting extra air or vapour into the intakepossible
• Wiring or connector fault in the idle control valve or throttle body circuit, or a poor earthpossible
• Faulty airflow, intake pressure or temperature sensor giving incorrect load readingspossible
• Throttle body adaptation lost or incomplete after battery disconnection or component replacement, or a fault in the control unitrare

How to diagnose

1. Read all stored codes and freeze frame data to see engine temperature, speed and load when the fault set, and check for other related codes
2. Check the live idle speed against the specified target and see whether it is stable, and whether it changes with electrical loads or air conditioning
3. Visually inspect intake pipework, vacuum hoses, brake servo hose, crankcase breather hoses and clamps for splits, perishing or looseness
4. Inspect the wiring and connectors at the idle control valve or throttle body for damage, corrosion or poor pin fit
5. Look for an intake leak using a smoke tester, and check that the purge valve and crankcase ventilation are not drawing in extra air
6. Inspect the throttle body bore and idle air passages for carbon build-up and check the throttle plate moves freely
7. Compare live data from the airflow and intake pressure sensors with expected values at idle and check the actuator responds to commands
8. Check battery and charging voltage and earth connections, then follow the manufacturer's procedure for throttle adaptation after any repair

How to fix

• Repair or replace leaking hoses, gaskets, clamps or seals found in the intake system
• Clean the throttle body and idle air passages using a suitable cleaner, following the manufacturer's procedure, then carry out the throttle adaptation or relearn
• Replace the idle air control valve or throttle body if it sticks or fails the actuator tests
• Replace a faulty purge valve or repair the crankcase ventilation system
• Repair damaged wiring, connectors or earths in the idle control circuit
• Replace any faulty airflow or pressure sensor confirmed by testing

Can I keep driving?

This code for other makes

• P0505AudiDefective Idle Air Control Motor, Intake Manifold Vacuum leaks, Carbon buildup in the Throttle Body air passages

Nearby codes

• P0504GenericBrake Switch A/B Correlation
• P0506GenericIdle Control System RPM - Lower Than Expected