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Code P505 2000 Honda Civic EX

Hi, I bought my 15 years old son a 2000 Honda Civic Ex. It has a P505 code, I have checked for vacuum leaks and have replace 4 of the Idle air control vales, 2 used from the junk yard and 2 new from ebay. I have done the ECU reset many times the stupid code keeps coming back. I can not get rid of this code, I am ready to pull my hair out. I am desperate for help.
Thank you all in advance.

There are other things that will set that code, like carbon buildup in the throttle body or vacuum leaks in the intake manifold.
The next time you have a trouble code, google that code and find all the causes and get diagnostic advice.

FSB with fix is in mid-article

Hi, thanks for the reply. I have take out the throttle body and cleaned it. I also have checked for vacuum leaks. Replaced the pcv valve. This car however has a cold air intake everything is hooked up properly.
Completely stumped.

Did you buy this car with that “cold air intake” or installed it later?

If you bought car with cold intake installed, did it have P505 or is it something popping up later?

Also make sure the coolant is running at the correct temperature when the engine is warm. A thermostat not operating properly and inaccurately regulating the coolant temp might result in this symptom.

We bought it like that and the code was there. The had bought and installed a new IAVC. THE STUPID CODE.

The coolant is at between 86-89° C. The normal range.

The car had p131 and p420 code when we bought it. I replace the catalytic converter and the o2 sensor. IRAs passes emissions m just fine.

I would entertain an idea about “cold intake” having substantially lesser resistance than stock one.
If junk-yard is around and getting stock intake is an option, it might be something to try?

Does this engine have a gadget that allows you to adjust the idle rpm? Like on my Corolla there’s an idle air bleed adjustment. If so that must be adjusted per the manufacturer’s procedure for the engine to idle & run correctly. If it isn’t it confuses the computer. An undiagnosed vacuum leak is the other likely explanation. It’s not so easy a thing to check. First step is to use a hand held vacuum pump/gauge and test every single thing that plugs into the intake manifold as a vacuum source, pump up each one and make sure they all hold vacuum. MAP sensor (if applicable) power brake booster. Everything that senses or uses manifold vacuum must hold vacuum. After that you have to look for problems with devices that automatically route intake manifold vacuum. The power steering pump might be one, it varies car to car. A faulty pcv valve can create the equivalent of a vacuum leak too. If it’s not of that and the idle air control gadget is working correctly, then you’d have to suspect the computer itself may be the problem.