P0505 moderate

Idle Control System Malfunction

What does P0505 mean?

The P0505 code means the vehicle's onboard diagnostic system has detected: Idle Control System Malfunction. This is a moderate severity code.

Common Symptoms

  • Rough idle
  • Idle too high or too low
  • Engine stalling at idle
  • Idle fluctuation between 400 and 1500 RPM

Probable Causes (Ranked by Likelihood)

  • Dirty or failed idle air control (IAC) valve Very High
  • Vacuum leak causing an uncontrolled idle High
  • Dirty throttle body with carbon buildup High
  • Failed throttle position sensor Moderate

Step-by-Step Diagnostic Procedure

  1. Remove the IAC valve and clean its pintle and housing with throttle body cleaner. Carbon buildup on the valve prevents proper idle control.

  2. Inspect all vacuum hoses for cracks or disconnection.

  3. Clean the throttle body -- carbon buildup around the throttle plate causes erratic idle, especially on direct-injection engines.

  4. Monitor IAC counts on a scan tool. Excessively high counts (above 80-100) indicate the IAC is working overtime to compensate for a vacuum leak.

Frequently Asked Questions

Can cleaning the IAC valve fix P0505?

Often yes. Carbon deposits prevent the IAC valve pintle from moving freely, causing inconsistent idle control. Cleaning with throttle body cleaner is the first step and may resolve the code without replacing the valve.

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