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Honda Civic with P0505 code
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NaymzJaymz
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Apr 10, 2023, 2:20 PM
Post #1 of 13
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Honda Civic with P0505 code
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2000 Honda Civic
260K
D16Y8 W/5 speed MT
Hi, this vehicle has code P0505. It was purchased with high miles and with this code intermittently occurring. I recently changed the head gasket due to the vehicle failing the combustion leak test. I was hoping this might help as I've heard that gasses in the coolant can cause this code. I was proud of myself over the HG job as it was the most invasive automotive procedure I've ever done, but I still have my idle issue. The car runs great otherwise. After the engine has warmed up and I come a long stoplight with engine running, the idle gets ragged and I get a jolty ride and the CEL comes on. I've exhaustively checked for vacuum leaks with a smoke tester, and it of course has new coolant which I extensively purged. I also tested around the intake gasket surface with propane with no stalling. Should I now suspect the IAC itself? The one that's there now seems pretty shiny, like it's not old. I bought a cheap Ebay knock-off IAC(not smart I know)and it was even worse with massive idle surges, so I put the old one back on. I've heard that Honda idle issues can drive a guy nuts, and I'm learning that. Thanks for any help I can get.
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Sidom
Veteran
/ Moderator
Apr 10, 2023, 8:38 PM
Post #2 of 13
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Re: Honda Civic with P0505 code
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Other than the code, is there any other running problems?
If not, then clear out the code and see if it comes back and how long it takes to come back.
For any type of diagnosing this code you are going to need a scan tool that supplies a datastream.
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NaymzJaymz
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Apr 11, 2023, 4:33 AM
Post #3 of 13
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Re: Honda Civic with P0505 code
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As I mentioned in my OP, the car runs great until at times I have to stop at a lengthy stoplight, then the CEL comes on with the P0505 code. The performance is then jolty. After the engine has been shut down and restarted, it runs fine again. I would also say that it idles too high at curb idle as well. I have cleared the code many times in the time I've owned it. There have also been times when the code has cleared on its own until it inevitably returns. My scanner does live data. Thanks.
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Hammer Time
Ultimate Carjunky
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Apr 11, 2023, 4:35 AM
Post #4 of 13
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Re: Honda Civic with P0505 code
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With the high mileage you have on this thing it's possible the throttle body is just worn out but I would try cleaning it first.
Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carb cleaner. Be sure to spray some into the small holes next to the throttle plate.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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NaymzJaymz
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Apr 11, 2023, 5:50 AM
Post #5 of 13
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Re: Honda Civic with P0505 code
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Thanks HT, without posting an extremely OP, I could've elaborated more. I've disassembled everything you mentioned and cleaned it as you mentioned(more than once). I can't help but feel there is a vacuum leak, could it be the intake manifold, even though I've checked thoroughly? Is it possible it could be the TPS, or would I be getting a code specific to that? Thanks.
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Hammer Time
Ultimate Carjunky
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Apr 11, 2023, 6:13 AM
Post #6 of 13
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Re: Honda Civic with P0505 code
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Yes, it could definitely be a vacuum leak. A worn throttle shaft in the throttle body could also be the source of that leak.
I would suggest doing a smoke test on the intake system to find any leaks.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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NaymzJaymz
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Apr 16, 2023, 12:08 PM
Post #7 of 13
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Re: Honda Civic with P0505 code
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I'm sorry to be nag about this issue. I've smoke tested and propane tested everything until I'm blue in the face. Is it possible it could be the IAVC itself? Do you now a way of testing it? Thanks.
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Hammer Time
Ultimate Carjunky
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Apr 16, 2023, 12:11 PM
Post #8 of 13
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Re: Honda Civic with P0505 code
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Definitely could be the IAC. That's usually the go to once you eliminate everything else.
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NaymzJaymz
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Apr 22, 2023, 8:23 AM
Post #9 of 13
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Re: Honda Civic with P0505 code
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As I mentioned in the OP, I tried a cheap Ebay knock off IAVC that resulted in even worse performance. The car had massive idle surges like I was sitting in pressing the accelerator and releasing. Do you think the part itself might be the reason? If I bought Honda OEM, would I have a better chance?
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Hammer Time
Ultimate Carjunky
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Apr 22, 2023, 8:30 AM
Post #10 of 13
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Re: Honda Civic with P0505 code
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These idle speed controls have coolant running through them to help regulate idle through engine temp. If you have air pockets in the coolant you will get the erratic idle you refer to.
You have to make sure the coolant is full and all air is bled out when the IAC is installed.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Sidom
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Apr 22, 2023, 12:38 PM
Post #11 of 13
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Re: Honda Civic with P0505 code
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As HT said, these have coolant running through them. It's been years, but my experience with these is the old coolant gets in there and gums the gears up and then you get the problem that you're describing. Normally a quality name brand will work well. I've never really messed around with those cheap Chinese knockoffs, but I've seen a lot of problems with them. It's always a crapshot.
If you have a vacuum leak bad enough to cause this problem "usually"you'll get the corresponding p0171 lean code for the vacuum leak, but like anything in automotive nothing is 100%.
One thing you can do is check base idle. You do this by blocking off the passage in the throttle body that feeds the IAC. Then you start the engine and it should run in the range of around 400 RPM. If it continues to run at a higher idle, then you do have some false air getting it somewhere.
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NaymzJaymz
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Apr 23, 2023, 1:34 PM
Post #12 of 13
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Re: Honda Civic with P0505 code
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Thank you, sir.
I've purged the coolant with a purge kit until I'm blue in the face. When I loosen the snorkel and put my finger over that air passage hole you mention(that goes to the IAVC), it does just like you said. It drops to a low idle. One thing that perplexes me is that the IAVC on the vehicle looks pretty new and has no build up in it. I've never gotten the 171 code, only 505. Is it time to get an OEM IAVC? As I outlined in the OP, I've exhaustively smoke tested and propane tested for vacuum leaks. Thanks.
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Hammer Time
Ultimate Carjunky
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Apr 23, 2023, 1:49 PM
Post #13 of 13
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Re: Honda Civic with P0505 code
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Looks like it's time.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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