Buzzing humming sound from IACV

[IM-32-FK]

For the past few months I’ve had this buzzing humming sound coming from the IACV motor area on the 25detneo. Only starts when coolant temp goes up to about 70degree from cold start. When you turn the car off, it still sounds for a couple of seconds with a ‘dying’ sound.

Here’s a video of what I mean 

 

car still runs perfect like nothings wrong. I cleaned out the IACV many months ago including the motor(I used contact electrical cleaner for the motor). I could’ve sworn I put it back together how it came out.

I did that thing were you get a hose and put one side in your ear and the other side where the sound is coming from and when I touched it against the IACV motor it was the loudest.
does this sound like a IACV motor dying? Or could it be something else related to it? Cheers 
 

[GTSBoy]

Video is not helping. Sounds like an engine.

The IACV will not respond usefully until the coolant heats up enough to close the cold fast idle circuit. At that point the IACV will be able to start to control the idle speed. So it's not surprising that you hear nothing until 70°C, because up until then the IACV is probably driven hard up against the closed position.

For all I know, the IACV always makes some noise. Is this a new thing? How loud is it really?

What does your ECU tell you (via Consult) about the number of "steps" that the IACV is operating at, below 70 and above when it starts making noise?

 

[IM-32-FK]

On 25/11/2021 at 5:46 PM, GTSBoy said:

Video is not helping. Sounds like an engine.

The IACV will not respond usefully until the coolant heats up enough to close the cold fast idle circuit. At that point the IACV will be able to start to control the idle speed. So it's not surprising that you hear nothing until 70°C, because up until then the IACV is probably driven hard up against the closed position.

For all I know, the IACV always makes some noise. Is this a new thing? How loud is it really?

What does your ECU tell you (via Consult) about the number of "steps" that the IACV is operating at, below 70 and above when it starts making noise?

 

If you watch the video, you’ll notice a loud buzzing sound, especially when I’m nearing the IACV. Hey, it might of been around before, but now the buzzing sound is even overriding the sound of the engine. Is it really loud, enough that I can hear it when I’m sitting in my car even with the exhaust sound. I don’t have a consult cable. Happened around the time I did multiple coolant radiator flushes, changed the alternator. Someone said it could be cause of the alternator, cam belt or power steering belt too tight but I checked and they are good. When I unplug the iacv motor, the sound still remains.

[GTSBoy]

Oh, then it is probably a vacuum/flow leak associated with the air path through the cold idle valve.

[GTSBoy]

Sorry, without context..... I meant the above to follow from

On 11/25/2021 at 5:35 PM, IM-32-FK said:

When I unplug the iacv motor, the sound still remains.

 

[IM-32-FK]

On 25/11/2021 at 6:07 PM, GTSBoy said:

Sorry, without context..... I meant the above to follow from

 

Could you tell me which hoses I could possibly have a vacuum leak from? I checked the main input hose going from the j pipe to the iacv looks good

 

[GTSBoy]

I meant internally. The cold start valve is a deliberate vacuum leak (from a certain point of view). It's not a "problem" vacuum leak, because it is drawing filtered and metered air.

What I mean is that the valve might be not closing properly, leaving a small opening that makes a noise, like a whistle or a trumpet, as the air gets pulled through. The air is doing near sonic velocities while going through. Small holes can be exceedingly noisy.

I thought this might be the case because the noise is clearly not the motor having an electric fit, if the noise continues when you unplug it.

[IM-32-FK]

On 25/11/2021 at 6:30 PM, GTSBoy said:

I meant internally. The cold start valve is a deliberate vacuum leak (from a certain point of view). It's not a "problem" vacuum leak, because it is drawing filtered and metered air.

What I mean is that the valve might be not closing properly, leaving a small opening that makes a noise, like a whistle or a trumpet, as the air gets pulled through. The air is doing near sonic velocities while going through. Small holes can be exceedingly noisy.

I thought this might be the case because the noise is clearly not the motor having an electric fit, if the noise continues when you unplug it.

So you reckon I should replace the whole IACV? Also if the valve isn’t closing properly, wouldn’t that mean it would idle higher than usual? It sits tight at 900rpm.

[GTSBoy]

Well, now you can look to test it by getting it warm, then stopping the car. Then disconnect and block both the hose and the IACV to prevent any air going through it. Start it back up and see if it goes quiet. You might need to open another vacuum leak into one of the small ports on the plenum to give it enough air to idle. You could attach a length of hose to that to take noise of that leak away so it doesn't interfere with the experiment.

If you find that the noise was an internal air noise. You might try to clean the cold start valve part of the IACV a bit more.

Otherwise, rather than replacing the IACV, I would convert to Haltech and e-throttle as much better alternative, fully justified by the failure of the IACV!!!!!

[joshuaho96]

If you choose to retain the stock AAC valve and want to buy a new one the cheapest source I found in the US was PartsForNissans: https://www.partsfornissans.com/p-jdm-nissan-r34-skyline-rb25det-neo-idle-air-control-valve-b3781aa500

[IM-32-FK]

On 25/11/2021 at 7:11 PM, GTSBoy said:

Well, now you can look to test it by getting it warm, then stopping the car. Then disconnect and block both the hose and the IACV to prevent any air going through it. Start it back up and see if it goes quiet. You might need to open another vacuum leak into one of the small ports on the plenum to give it enough air to idle. You could attach a length of hose to that to take noise of that leak away so it doesn't interfere with the experiment.

If you find that the noise was an internal air noise. You might try to clean the cold start valve part of the IACV a bit more.

Otherwise, rather than replacing the IACV, I would convert to Haltech and e-throttle as much better alternative, fully justified by the failure of the IACV!!!!!

Hey is there by any chance that it could be the intake manifolD gaskets, either from top runners to bottom runners or bottom runners to block- even though the car runs perfect? I was looking at various threads on google for similar issues and some said pcv valve but most said intake gaskets. I removed the pcv valve and blew into it from both sides with my lips sealed around it and air didn’t come out from either side. Also if I am to change the intake gaskets, I’ve already got MLS ones. I was checking the service manual and it says nothing about putting gasket glue anywhere even the coolant port. What do you Recommend I do?

[IM-32-FK]

Oh and btw, this is how it sounds before the buzzing humming noise comes on. If you listen to this video and the video in my initial post, you’ll definitely hear the difference in sound

 

Edited November 25, 2021 by IM-32-FK

[GTSBoy]

Won't be the manifold gaskets. If it was it would be howling on boost.

I can hear the tone in the first video now. There's no way that you would know it was unusual without the 2nd video. There's no way to identify it from the sound. Just sounds like any 10 other engine bays.

[IM-32-FK]

On 25/11/2021 at 10:17 PM, GTSBoy said:

Won't be the manifold gaskets. If it was it would be howling on boost.

I can hear the tone in the first video now. There's no way that you would know it was unusual without the 2nd video. There's no way to identify it from the sound. Just sounds like any 10 other engine bays.

Ok so I got it, it’s the whole IACV unit I need to replace. I’ll let you know how it goes.

[GTSBoy]

I don't think I'd replace it. I might buy a spare for if/when it eventually dies, but I wouldn't swap it out just 'cause it's making a noise. I'd try to clean it again as the very first measure.

But I don't plan on buying a spare for mine either. Because if mine dies, I will definitely throw an ECU and e-throttle at the car.

[Rusty Nuts]

On 11/25/2021 at 9:31 PM, IM-32-FK said:

Ok so I got it, it’s the whole IACV unit I need to replace. I’ll let you know how it goes.

And include the price when you buy it, I checked some years ago, and it cost an arm and a leg, MY advice is clean it again and ensure its reassembled correctly

[IM-32-FK]

On 26/11/2021 at 1:57 PM, Rusty Nuts said:

And include the price when you buy it, I checked some years ago, and it cost an arm and a leg, MY advice is clean it again and ensure its reassembled correctly

I cleaned it out thoroughly, but when I took the motor out a spring and something else fell out of it. I remember putting them both back in, but I’m not sure if there is some procedure to do it properly. If I take the motor out, can you tell me how to assemble it back ? Also I never used any gasket sealant on the gasket, as there was none before

Edited November 26, 2021 by IM-32-FK

[Rusty Nuts]

On 11/26/2021 at 6:54 PM, IM-32-FK said:

If I take the motor out, can you tell me how to assemble it back ?

Nissan Stagea Rb25 Neo IACV clean on youtube

[IM-32-FK]

On 27/11/2021 at 12:53 PM, Rusty Nuts said:

Nissan Stagea Rb25 Neo IACV clean on youtube

I’ve seen that and that guy never said anything about the motor. I took the motor out and cleaned it out with electric contact cleaner. I thought while it’s out I might as well clean it. I guess I shouldn’t have.

Edited November 27, 2021 by IM-32-FK

[joshuaho96]

On 11/26/2021 at 10:25 PM, IM-32-FK said:

I’ve seen that and that guy never said anything about the motor. I took the motor out and cleaned it out with electric contact cleaner. I thought while it’s out I might as well clean it. I guess I shouldn’t have.

AFAIK in the RB26 section of the service manual it explicitly says not to take apart the AAC valve. If you took it apart once there's no harm in taking it apart again to see if you can save it.