DTC P0505: Malfunction in Idle Control System

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 are not operating.
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 IAC valve 3P connector.
Does the engine speed increase or fluctuate?
1. YES: Adjust the idle speed (see Idle Speed Adjustment ). If the idle speed will not adjust properly, clean the passage in the throttle body, and then adjust it again.
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: Putting Your Fingers On The Lower Port In The Throttle Body
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Does the engine speed drop?
1. YES: Check the idle speed (see Idle Speed Adjustment ). If it's out of specification, replace the IAC valve.
2. NO: Check for vacuum leaks with the throttle valve completely closed, and repair as needed.