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: headlights, blower fan, rear defogger, radiator fan, and air conditioner off.
Is the engine running at 700 to 800 rpm?
1. YES - Intermittent failure, system is OK at this time.
2. NO - If the idle speed is less than 700 rpm, go to step 3; if it's higher than 800 rpm, go to step 4.
Disconnect the idle air control (IAC) valve 3P connector.
Does the engine speed increase or fluctuate?
- YES - Check the idle speed with 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 (see THROTTLE BODY DISASSEMBLY/REASSEMBLY ).
- NO - Replace the IAC valve (see THROTTLE BODY DISASSEMBLY/REASSEMBLY ).
Turn the ignition switch OFF.
Remove the intake air duct from the throttle body (see AIR CLEANER REMOVAL/INSTALLATION ).
Start the engine, and let it idle.
Put your fingers on the lower port (A) in the throttle body.

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

Does the engine stall?
1. YES - Check the idle speed with 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 (see THROTTLE BODY DISASSEMBLY/REASSEMBLY ).
2. NO - Check for vacuum leaks these parts:
  - PCV valve
  - PCV hose
  - EVAP canister purge valve
  - Intake manifold
  - Throttle body
  - Brake booster hose