P0505 Toyota Highlander
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 Toyota Highlander 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 Toyota Highlander.
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 Toyota Highlander.
Common Causes on Toyota Highlander
- Idle air control (IAC) valve malfunction — carbon buildup preventing proper operation
- IAC valve motor failed
- Vacuum leak at IAC valve gasket or hose
- Throttle body carbon buildup on models with electronic throttle (replaces traditional IAC)
Symptoms
- Erratic idle speed — surging between 500 and 1500 RPM
- Engine stalling at idle, especially when coming to a stop
- High idle speed that won't come down
- Check Engine Light on
Notes for Toyota Highlander
Newer Toyota models with electronic throttle bodies do not have a separate IAC valve — P0505 on these models points to the throttle body itself.