DTC P0505 - Idle Control System (Civic)

NOTE: If DTCs P1508 or P1509 are also stored, repair those DTCs first.

Start engine. Raise and hold engine speed at 3000 RPM with transmission in Park or Neutral, until cooling fan comes on. Let engine idle. Using scan tool, ensure throttle position is approximately 10 percent with throttle fully closed and engine coolant temperature is 194-205°F (90-96°C). If throttle position or engine coolant temperature are not within specification, repair faulty sensor circuit. Using scan tool, check engine speed. See ENGINE MECHANICAL in ON-VEHICLE ADJUSTMENTS article. If engine speed is within specifications, system is okay at this time. Problem is intermittent.
If engine speed is 550 RPM or less, go to step 3). If engine speed not is 550 or less, turn ignition off. Remove air intake duct from throttle body. Start engine and allow it to idle. Place a finger on upper port in throttle body. If engine speed does not drop, check for vacuum leaks and ensure throttle valve is completely closed. Repair as necessary. If idle speed drops, adjust idle speed to specification. See ENGINE MECHANICAL in ON-VEHICLE ADJUSTMENTS article. If idle speed will not adjust to specification, replace IAC valve.
Disconnect IAC valve connector. On auto transaxle and D16Y7 engine models, if engine speed does not increase, replace IAC valve. If engine speed increased, adjust base idle speed. Refer to the ENGINE MECHANICAL in ON-VEHICLE ADJUSTMENTS article. If engine speed does not adjust to specification, clean throttle body ports. On models with D16Y5 and D16Y8 engines and manual transaxle, if engine speed does not drop or engine stalls, replace IAC valve. If engine speed drops or engine stalls, adjust base idle speed. See ENGINE MECHANICAL in ON-VEHICLE ADJUSTMENTS article. If engine speed does not adjust to specification, clean throttle body ports.