Generic OBD2 code · Idle control

P0505: Idle Air Control System

The engine computer cannot control idle speed as commanded through the idle air control (IAC) system.

CodeP0505
SystemIdle control
Typical urgencyModerate to high
Can I keep driving?Usually drivable, but stalling at stops can be a hazard, so diagnose it soon.

What does P0505 mean?

On vehicles with an idle air control valve, the ECM opens and closes the valve to let a measured amount of air bypass the throttle plate and hold a steady idle.

When the actual idle speed does not follow the commanded idle speed, or the valve circuit has a fault, the ECM stores P0505.

Common symptoms

  • Check engine light on
  • Idle speed too low, with possible stalling at stops
  • Rough idle
  • In some cases a high idle

Common causes

The causes below are the ones commonly seen with P0505. The actual cause can vary by vehicle, engine and mileage, so treat this list as a starting point, not a diagnosis.

  • A faulty idle air control valve or motor
  • Carbon buildup in the throttle body air passages
  • Wiring or connector problems at the idle air control valve

What to check with a scanner

  • In Live data, compare actual idle rpm with the desired idle rpm, if your vehicle reports it.
  • Inspect the throttle body and idle air passages for carbon buildup.
  • Check the idle air control valve connector and wiring.
  • Some vehicles need an idle relearn after cleaning or replacing parts. Follow your service information.

How to read and clear P0505 with OBD Master Pro

  1. Plug in your adapter. Connect a generic ELM327 (or ELM329) OBD2 adapter to the diagnostic port, usually under the dashboard on the driver's side. Bluetooth Classic, Bluetooth LE, Wi-Fi and USB OTG adapters are supported.
  2. Switch the ignition on. Turn the key to ON or start the engine, depending on your car.
  3. Connect in OBD Master Pro. Open the app, go to Connection and pick your adapter. Classic Bluetooth adapters connect from the Bluetooth tab, Bluetooth LE adapters from the BLE tab with no pairing needed. Use the generic OBD2 / EOBD profile or your car's brand profile.
  4. Read the codes. Open the fault codes screen to see stored, pending and permanent codes. Confirm P0505 is listed and note any other codes, since they often explain the cause.
  5. Check the details. Look at freeze frame data, Live data and, where your car supports it, Mode 06 test results (see the checks above).
  6. Fix, then clear. After the repair, clear the codes to turn off the check engine light. Clearing also resets the emissions readiness monitors, so drive normally and check the readiness screen before any inspection. Permanent codes cannot be erased with a scan tool; they clear on their own once the car's self test passes.

Tip: you can also look up P0505 and other codes in the app's DTC search without connecting to a car. If your adapter will not connect, use Connection > Share connection log and email it to support. Many cheap ELM327 clones only handle basic engine OBD2, which is all you need for P0505.

When to see a mechanic

Get professional help if any of these apply:

  • The engine stalls at stops
  • The idle stays wrong after cleaning the throttle body
  • You need circuit tests on the IAC valve

If you are unsure, a qualified technician can confirm the cause with tests such as smoke testing, pressure testing or scope readings. Clearing a code does not repair the fault.

P0505 FAQ

Can I drive with P0505?

Usually, but stalling at stops can be dangerous in traffic. Get it checked soon.

Can cleaning the throttle body fix P0505?

Sometimes. Carbon in the throttle body passages is a common cause, and an idle relearn may be needed afterward on some vehicles.

Should I replace the IAC valve right away?

Check the wiring and look for carbon in the throttle body first. Replacing the valve when carbon buildup is the real cause is a common misdiagnosis.

Check P0505 on your own car

OBD Master Pro turns your Android phone and a generic ELM327 adapter into a code reader: read and clear codes, view freeze frame and live data, and check emissions readiness.

Get it on Google Play

Related guides

Check engine light on: what to do · How to read an OBD2 code (P, B, C, U) · Stored, pending and permanent codes and freeze frame · OBD2 readiness monitors explained · OBD2 glossary · OBD2 by car brand

Sources

Published . Updated . This guide is general information for generic SAE codes. Always follow the service information for your specific vehicle.