DTC P0505: Idle Control System Malfunction

NOTE: If DTC P1519 is stored at 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.
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 730+/-50 RPM?
1. YES -Intermittent failure, system is OK at this time.
2. NO -If the idle speed is less than 680 RPM, go to step 3; if it's 780 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 -Adjust the idle speed (see Idle Speed Adjustment ). 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 finger on the lower port (A) in the throttle body.

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

Does the engine speed drop below 780 RPM?
1. YES -Adjust the idle speed (see Idle Speed Adjustment ). If the idle will not adjust properly, replace the IAC valve (see THROTTLE BODY DISASSEMBLY/REASSEMBLY ), and then adjust the idle.
2. NO -With the throttle valve completely closed, check for vacuum leaks, and repair as necessary.