DTC P0505: Idle Control System Malfunction

NOTE: If DTC P1519 is stored at the same time as DTC P0505, troubleshoot DTC P1519 first, then recheck for DTC P0505.

Start the engine. Hold the engine at 3,000 RPM with no load (in Park or neutral) until the radiator fan comes on, then let it idle.
Check the engine speed at idle with no-load conditions: headlights, blower fan, rear window defogger, radiator fan, and air conditioner off.
Is the engine running at 650+/-50 RPM?
1. YES - Intermittent failure, system is OK at this time.
2. NO - If the idle speed is less than 600 RPM, go to step 3; if it's 700 RPM or higher, go to step 4.
Disconnect the idle air control (IAC) valve 3P connector.
Does the engine speed increase or fluctuate?
1. YES - Check the idle speed (see Idle Speed Inspection ). If the idle will not adjust properly, clean the passage in the throttle body, and then adjust the idle.
2. NO - Replace the IAC valve.
Turn the ignition switch OFF.
Remove the intake air duct from the throttle body.
Start the engine, and let it idle.
Put your fingers on the lower port (A) in the throttle body.

Fig 1: Blocking Lower Port In Throttle Body
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Does the engine stall?
1. YES - Check the idle speed (see Idle Speed Inspection ). If it's out of specification, replace the IAC valve.
2. NO - Check for vacuum leaks. Make sure the throttle valve is completely closed, and repair as necessary.