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 (2000-2003 models)
- If DTC P1519 is stored at the same time as DTC P0505, troubleshoot DTC P1519 first, then recheck for DTC P0505.
- Before you troubleshoot, record all freeze data and review the general troubleshooting information (see GENERAL TROUBLESHOOTING INFORMATION ).
- Start the engine. Hold the engine speed at 3,000 RPM without load (in Park or neutral) until the radiator fan comes on, then let it idle.
- Check the engine speed at idle without load condition: headlights, blower fan, rear defogger, radiator fan, and air conditioner off.
Is the idle speed 900+/- 50 RPM?
- YES -Intermittent failure, system is OK at this time.
- NO -If the idle speed is less than 850 RPM, go to step 3; if it's 950 RPM or higher, go to step 4.
- Disconnect the IAC valve 3P connector.
Does the engine speed increase or fluctuate?
- YES -Check the idle speed under different load conditions (electrical, A/C, gear position, P/S, etc.) (see IDLE SPEED ADJUSTMENT ). If it's out of specification, clean the ports in the throttle body.
- NO -Replace the IAC valve (see THROTTLE BODY DISASSEMBLY/REASSEMBLY ).
- Turn the ignition switch OFF.
- Remove the intake air duct from the throttle body.
- Start the engine, and let it idle.
- Block both the round bypass port (A) and the rectangular IAC port (B) in the throttle body with your fingers.
Courtesy of AMERICAN HONDA MOTOR CO., INC.
Does the engine stall?
- YES -Check the idle speed under different load conditions (electrical, A/C, gear position, P/S, etc.) (see IDLE SPEED ADJUSTMENT ). If it's out of specification, replace the IAC valve.
- NO
-Check for vacuum leaks at these parts:
- PCV valve
- PCV hose
- EVAP canister purge valve
- Intake manifold
- Throttle body
- Brake booster hose
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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.
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