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Idle issues after replacing the head gasket

Tiny
DANVEP5014
  • MEMBER
  • 1998 HONDA CIVIC
  • 1.6L
  • 4 CYL
  • 2WD
  • MANUAL
  • 273,000 MILES
After I replaced my head gasket, the car had an issue idling. The idle hunts and stays at around 1,500 RPM's when it is usually around 500. I replaced the throttle body with one from the junkyard and it fixed it for a couple of days but now it's the same problem. I've replaced the MAP sensor, throttle position sensor, and I've gone through 3 IAC valves. I'm at a loss and don't know what to do. No vacuum leaks either. I've plugged all the ports to test.
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Wednesday, November 18th, 2020 AT 2:14 PM

11 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Okay. Couple things. First have you checked for vacuum leaks using the methods in this guide? Namely the use of spray cleaner around the engine.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Also, since you opened the cooling system we need to make sure there is no air in the system. When you are bleeding the air out, make sure you use a spill free funnel as shown in the picture. This will ensure you can work out the air pockets. Then follow these steps.

1. Turn the heat to hot and fan off. This way coolant will go through the heater core but the heater control valve will not close. This could cause an air pocket.
2. Loosen the bleeder screw under the throttle linkage. Should be a 12 mm bolt.
3. Fill the cooling system until the coolant comes out of the bleeder.
4. Top off the reservoir and then the radiator so that the funnel has a small amount of coolant.
5. Run engine at 2500 RPM until the fans come on.
6. Top off coolant again.

If this seems to work but then starts again a couple days later, I suspect you a leak in the cooling system allowing in more air.
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Wednesday, November 18th, 2020 AT 4:05 PM
Tiny
DANVEP5014
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  • 7 POSTS
Okay, so I attempted to bleed the air out of the system. There is no bleeder bolt on my engine around there, so what I did was jack the front of the car up and turned on the heat with the fan off. I revved up the engine and had tons of air coming out. I think through this process, I introduced more air. I took it for a drive and the temperature gauge goes from normal to below normal and pretty far towards the bottom sometimes. I checked for vacuum leaks and again, I had nothing. Is there a bleeder somewhere else on my engine (d16y7)?
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Wednesday, November 18th, 2020 AT 4:46 PM
Tiny
DANVEP5014
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  • 7 POSTS
I've looked and it's definitely not air in the cooling system. I made sure to get all air out and it is still the same issue. I even again checked for vacuum leaks and still there are none. The codes I've been getting is code p0505 for the idle and then occasionally a code p0420 but if I clear that, it goes away for a while. The part that confuses me is that it worked great for about 300 miles when I replaced the throttle body, but now its doing it again. Even with all new sensors. I've looked at everything and it checks out. I'm completely baffled and at a complete loss. Very frustrating.
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Wednesday, November 18th, 2020 AT 6:11 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Okay. That is great info and I am sorry I didn't ask for codes before. Here is the testing for this code that we need to run through.

It may not be air in the system but this could still be related to the cooling system. Let's do this testing and go from there. Thanks
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Wednesday, November 18th, 2020 AT 6:24 PM
Tiny
DANVEP5014
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So I just finished the testing, everything checked out until I got to the IAC valve testing. When I put my finger on the lower port to cover it, my rpms do drop, but not much. So I put my hand over the throttle body to choke it out, and it does die, but it sounds like its sucking in coolant from the IAC valve. Would the gasket have possibly caused this? I did change the gasket several times.
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Wednesday, November 18th, 2020 AT 6:54 PM
Tiny
DANVEP5014
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  • 7 POSTS
Definitely not the IAC gasket either. This car is really getting the best of me.
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Thursday, November 19th, 2020 AT 6:30 AM
Tiny
KASEKENNY
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How often has the P0420 been popping up? The reason is, that it could cause some engine performance issues so we should run through this testing as well just to see if the code comes back. If the three way converter has failed, it could cause an engine imbalance which would lead to the idle issues. When you are clearing the code, it doesn't come back right away because it has to go through the needed drive cycle to fail again. So running this test should get it to set again. If it does, we should address that and see if it addresses the idle issues as well.
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Thursday, November 19th, 2020 AT 7:29 PM
Tiny
DANVEP5014
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I drove it around 150 miles today. It looks like the catalytic converter is good. Light didn't come back on. I plugged up all the vacuum ports and installed the OEM IAC valve. Idles at around 1,000 rpm's now. The check engine light comes on with the code p0505 again. It's impossible to drive until I clear that code. It sounds like its definitely a faulty IAC valve. Ordered another one from AutoZone since it has a lifetime warranty. I guess I'll keep replacing them until I find one that idles correctly. I can't find the Denso original IAC valve anywhere. It seems to be the only one that works. I get the second IAC valve tomorrow and fingers crossed that it has the correct idle. Don't know where else I could get the Denso part.
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Thursday, November 19th, 2020 AT 7:56 PM
Tiny
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I agree and totally understand your frustration. It is hard to believe that you have that many faulty ones but I agree that if it passes those tests for that code then the IAC is the issue. Keep us posted but just to double check. Did you check for a vacuum leak with spray cleaner around the intake or did you just plug the ports?
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Friday, November 20th, 2020 AT 5:41 PM
Tiny
DANVEP5014
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I checked for vacuum leaks first, and then plugged the ports. My final thoughts is that the ECU is bad. My question is, if I get a new one, do I have to get it reprogrammed, or is it plug and play?
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Saturday, November 21st, 2020 AT 7:37 AM
Tiny
KASEKENNY
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They do need to be programmed but it looks like most all options that you have come pre-programmed so you should be good to go. I attached a screen shot showing some options.
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Sunday, November 22nd, 2020 AT 1:08 PM

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