P0505 Honda Civic
Idle Air Control System Malfunction · Powertrain Code · Medium · Repair: Easy
What is P0505?
The idle air control (IAC) system is not maintaining proper idle speed.
When the Honda Civic triggers code P0505 (idle air control system malfunction), it typically points to an issue in the powertrain system. Below you'll find the most common causes, symptoms, and repair options specific to the Honda Civic.
This repair is rated easy, meaning basic tools, no lift needed.
Diagnostic data on this page is compiled from publicly available repair resources and technical service bulletins. Always have a qualified mechanic confirm the diagnosis before authorizing repairs on your Honda Civic.
Common Causes on Honda Civic
- Carbon-fouled Idle Air Control (IAC) valve
- Failed IAC valve motor
- Vacuum leak affecting idle speed control
- Dirty throttle body preventing proper idle airflow
Symptoms
- Erratic idle speed (hunting between 500-1500 RPM)
- Stalling at idle or when coming to a stop
- High idle speed that won't come down
- Check Engine Light on
Notes for Honda Civic
On newer Honda models with electronic throttle, this code relates to the throttle body rather than a separate IAC valve — clean the throttle body and perform the idle relearn.