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 under no-load conditions: headlights, blower fan, rear defogger, radiator fan, and air conditioner off.
Is it 700 +/- 50 rpm?
1. YES - Intermittent failure, system is OK at this time.
2. NO - If the idle speed is less than 650 rpm, go to step 3; if it's 750 rpm or higher, go to step 4.
Disconnect the 3P connector from the IAC valve.
Does the engine speed increase or fluctuate?
1. YES - Adjust the (base) idle speed (see Idle Speed Adjustment ). If it's impossible, clean the ports in the throttle body.
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 finger on the lower port (A) in the throttle body.

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

Does the engine speed drop?
1. YES - Adjust the idle speed (see Idle Speed Adjustment ). If it's impossible, replace the IAC valve.
2. NO - Check for vacuum leaks, make sure the throttle valve is completely closed, and repair as necessary.