P0505

What it means

P0505 on an Audi means the engine control unit has found that the idle speed is not following the target it has set, or the idle control system cannot hold it within limits. On many Audi engines the throttle body is electronically controlled and does the job of an idle air control motor, so a sticking throttle, extra unmetered air or carbon in the air passages can all set the code. The exact way idle is controlled depends on the model and engine.

Symptoms

• Idle speed too high, too low or hunting up and down
• Engine stalls or nearly stalls when coming to rest or when the air conditioning cuts in
• Rough idle
• Hesitation or poor response when pulling away from a stop
• Engine warning light on, sometimes with a throttle or limp-mode warning

Possible causes

• Carbon and dirt build-up in the throttle body bore or air passages, stopping it closing or moving correctlylikely
• Vacuum or intake leak after the airflow measurement, such as a split hose, a cracked intake pipe, a worn manifold seal or a leaking crankcase breather hoselikely
• Faulty or worn throttle body actuator or position sensor, or a failed idle air control valve on older models that have onepossible
• Faulty airflow meter or manifold pressure sensor giving wrong readingspossible
• Wiring or connector fault on the throttle body, such as corrosion, chafing or a loose plugpossible
• Throttle body needing adaptation or basic setting after cleaning, replacement or a battery disconnectionpossible
• Engine control unit fault or an outdated software calibrationrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting engine temperature, load and idle speed when the fault set, and look for related codes such as lean mixture or throttle faults
2. Check live data for target and actual idle speed, throttle position, airflow and short-term and long-term fuel trims at idle and at around 2,500 rpm
3. Inspect the intake system by eye for split or loose hoses, cracked pipes, a loose oil filler cap or dipstick and a leaking breather hose
4. Inspect the throttle body wiring and connector for damage, corrosion and poor contact, and check the battery and earth connections
5. Remove the intake pipe and check the throttle body bore and plate for carbon build-up, and check the plate moves smoothly without sticking
6. Smoke test the intake system to find leaks that cannot be seen, and check manifold seals
7. Compare the airflow meter and manifold pressure readings with expected values for the engine, and check the throttle body actuator and position sensor signals using the manufacturer's data
8. Check for a software update or technical bulletin for the model and engine if no mechanical fault is found

How to fix

• Clean the throttle body using a suitable cleaner and method for that model, taking care not to force the throttle plate, then carry out the throttle adaptation or basic setting
• Repair or replace any leaking hose, intake pipe, breather hose or manifold seal found
• Replace the throttle body or idle air control valve if it is worn, sticking or fails electrical or position checks
• Replace a faulty airflow meter or manifold pressure sensor once the readings are confirmed to be wrong
• Repair damaged wiring or connectors, then clear the codes and retest
• Update the engine control unit software only if an outdated calibration is confirmed as a cause for that model

Can I keep driving?

This code for other makes

• P0505GenericIdle Control System

Nearby codes

• P0501AudiDefective Vehicle Speed Sensor, Defective Speedometer, Vehicle Speed Sensor wiring or connector, Communication (CAN) bus problems, Defective transmission or differential Vehicle Speed Sensor drive gear
• P0506AudiDefective or sticking Idle Air Control Motor, Intake Manifold Vacuum leaks, Carbon buildup in the Throttle Body air passages, Defective Power Steering Pressure Switch