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.
DTC P0505: Idle Control System Malfunction
2004 Acura 3.5RLSECTION DTC P0505: Idle Control System Malfunction
WARNING: This page is about a different car, the 2003 Acura RSX. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
If DTC P1519 is also set, troubleshoot first before proceeding.
- Start engine and hold at 3000 RPM, with no load (in park or neutral), until cooling fan comes on. Using scan tool, check engine speed at idle with no load.
- If idle speed is 650-750 RPM (K20A2 engine) or 600-700 RPM (K20A3 engine), problem is intermittent. System okay at this time. If idle speed less than 650 RPM (K20A2 engine) or less than 600 RPM (K20A3 engine), go to next step. If idle speed is 750 RPM or more (K20A2 engine) or 700 RPM or more (K20A3 engine), go to step 4 .
- Disconnect Idle Air Control (IAC) valve 3-pin harness connector. If engine speed increases or fluctuates, check idle speed. See appropriate procedure under IDLE SPEED & MIXTURE in ON-VEHICLE ADJUSTMENTS article. If engine speed does not increase or fluctuate, replace IAC valve.
- Turn ignition switch off. Remove air cleaner from throttle body. Start engine and allow to idle. Place fingers over lower port inside throttle body. If engine speed does not drop below 750 RPM (K20A2 engine) or below 700 RPM (K20A3 engine), check for vacuum leaks. Ensure throttle valve is completely closed. If engine speed drops below 750 RPM (K20A2 engine) or below 700 RPM (K20A3 engine), check idle speed. See appropriate procedure under IDLE SPEED & MIXTURE in ON-VEHICLE ADJUSTMENTS article. If idle speed is out of specification, 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.