This problematic OBDII DTC code of P0505 can be difficult to trace down and correct to clear your Malfunction Indicator Lamp. Although there is a lot of information out on the Internet about this trouble code, most of it is misinformation. Today we’ll be showing you how to service your IAC to resolve the DTC P0505 trouble code.

Popular to contrary belief this OBDII trouble code is not a specific IAC trouble code, but in fact a trouble code for the Idle Control System. The Honda trouble code resolves to the CEL 14 which is Idle Control System Malfunction. We’ll be showing you how to service your IAC in a Honda to resolve this code.

The Idle Air Control Valve or IAC is responsible for adjusting the amount of air that flows past the throttle body to maintain idle. By opening and closing the valve, the Honda ECU can control the vehicle’s idle to allow more or less air into the intake manifold. There are two coolant lines that run to this IAC to help quiet it down during operation.

Symptoms of a P0505

• Erratic Idle
• Hunting Idle
• Low idle
• surging idle
• bad gas mileage

Possible Causes of P0505

• IAC mechanical malfunction
• Throttle body clogged port
• Intake manifold gasket leak
• Intake snorkel or hose leak
• Vacuum leak
• ECT sensor incorrect output
• Throttle Position Sensor incorrect output

To begin Idle Test

Start the engine and raise the engine speed (RPM) to 3000 and hold until the engine warms up and your radiator fan turns on. If your radiator fan does not turn on, there’s a problem with your Engine Coolant Temperature sensor, and that’s the true cause of your P0505 OBDII code.

Once your engine is warmed up, backprobe the throttle position sensor on your Honda by plugging in a scan tool or using a voltmeter on the back of your TPS harness.

In most Honda Civics this wire should be the middle pin or the black wire with pink stripe or white stripe. Check your operation manual or vehicle specific pinout for more information. Shown above is a 1996 Honda Civic EX VTEC TPS sensor.

When using a scan tool, the throttle deflection percentage should be around 10% with the throttle body in the closed position. With the throttle fully opened at WOT, the throttle position should read 100% or close to it. If you are using a voltmeter or multimeter to backprobe the signal wire, you should see near to 4.5 volts at Wide open throttle, and close to 1 volt at closed.

If you are using a scan tool, also check your coolant temp sensor, which should be hovering in the 190 ºF. If these values do not check out, there’s a different cause of your P0505 trouble code.

Check Idle

If your idle is above 550 RPM, you’ve got to check for vacuum leaks. Remove the intake snorkel and place your finger over the lower intake nipple port on the throttle body. The idle should drop and in many cases the engine will turn off completely because of the lack of idle maintenance.

If your idle does drop like it should, try to adjust the idle speed. If your idle does not stop, there’s something wrong with your IAC and it’s got to be removed and cleaned accordingly.

If your idle is below 550 RPM, try disconnecting the IAC valve to see if the idle increases. If it does increase try to adjust the base idle speed or go ahead and clean the IAC anyways.

Removing the IAC

It’s time we get to the real part of our how to service your IAC Guide, and the first step is to locate your IAC. The Honda IAC is located behind the intake manifold, usually bolted to the back of said manifold by two 12mm bolts. Once you’ve located the IAC valve in question, depress the metal clips and push off the coolant lines that run to it.

Allow these coolant lines to drip dry and then grab your 12mm wrench. You will be unbolting the two bolts that hold the IAC in place.

Once you’ve got the IAC connected, you can now clean it by clearing out or brushing out the holes in the intake manifold. Gently remove the IAC oring and inspect for any damage or tears. Now using WD-40 or Simple Green, spray inside the ports of your IAC to clean. Continue to clean until the fluid and debris has broken loose from the valve and seals inside the IAC.

Here are a few examples and part numbers for Honda IAC’s.

1997 Honda Civic – D16Y7 – 16022-P2A-J01 

1997 Honda Accord – F22B1 – 36450-P0B-A01

1993 Honda Civic – D16Z6 – EG – 36450-P28-A01

Once you have completed the cleaning process, go back to your intake manifold and ensure that the ports are clear of any debris or chunks. Try to clean outward and do not push foreign materials into the intake manifold that may become stuck.

When your Idle Air Control valve has dried, re-install and make sure to replace the IAC gasket. Clear your OBDII trouble code P0505 to reset your ECU and try to start your vehicle again. If your code or idle issues persist, sadly our How to Service your IAC article will not help you, and you must replace your IAC all together.

Have any questions about DTC P0505 or our How To Service your IAC Guide? Leave us a comment or question below!