Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Idle Air Control Valve: Highlander
2004 Toyota Celica GT, StandardSECTION Highlander
WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 2002 Toyota Tacoma, 2002 Toyota RAV4, 2002 Toyota Prius, 2002 Toyota MR2, and 2002 Toyota Highlander. However, it is still accessible from the selected car via links, so may be relevant.
- If problem exists in Idle Air Control (IAC) valve or wiring circuit, a Diagnostic Trouble Code (DTC) P0505 may be stored in Engine Control Module (ECM). See TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article for retrieving of DTCs.
- To test IAC valve operation, remove IAC valve from throttle body. See THROTTLE BODY under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - 4-CYLINDER article. Reinstall electrical connector on IAC valve.
- Turn ignition on. Check that valve on inside of IAC valve moves from half open to fully closed, fully open and then returns to half open within .5 seconds. See Fig 1. Turn ignition off. If IAC valve operates as specified, wiring circuit, Engine Control Module (ECM) and IAC valve are okay.
- If IAC valve operates as specified, wiring circuit, Engine Control Module (ECM) and IAC valve are okay. Clear any stored DTCs from ECM after checking IAC valve operation. See CLEARING DIAGNOSTIC TROUBLE CODES under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. If IAC valve does not operate, check wiring circuit between ECM and IAC valve. ECM is located behind glove box. For illustration of ECM location, see THEORY & OPERATION article. See WIRING DIAGRAMS article. If wiring circuit and ECM are okay, replace IAC valve.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.