P0505 GMC Terrain
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 GMC Terrain 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 GMC Terrain.
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 GMC Terrain.
Common Causes on GMC Terrain
- Dirty or failed idle air control (IAC) valve (older GM models with cable throttle)
- Carbon buildup in the throttle body bore
- Vacuum leak affecting idle speed control
- Failed electronic throttle body (newer drive-by-wire models)
Symptoms
- Erratic or hunting idle speed
- Idle too high or too low
- Engine stalls when coming to a stop
- Check Engine Light on
Notes for GMC Terrain
On older GM trucks with cable-operated throttle, cleaning the IAC and throttle body is often enough — newer drive-by-wire models require throttle body replacement.