DrCreosote

1990 4Runner 3VZE. It's been freshly rebuilt and I've taken way too long getting it in. When I drive it now, I get a funny little growl (or is it a fart?) from under the hood. It happens when I take my foot off the accelerator and it will stop once the vehicle stops.

I can get it to make the noise by working the accelerator under the hood. It seems to be coming from the right side of the engine where all that vacuum stuff is and I am somewhat certain that it is one of the vacuum operated devices making the racket, but I don't know which one and I don't know if it's a problem or just noisy.

I also made a recording of it and it's on my dropbox. You can hear it here

This forum has been invaluable to me and I appreciate every bit of help I've gotten here. Thank you in advance.

RSR

It sort of sounds like a whoopee cushion to be honest... Possibly you have a break in one of your vacuum lines or it's just shot causing it collapse/vibrate when air flow changes? LC Engineering sells a complete new vacuum line kit for ~$40. It's one of those maintenance items that is about due anyway due to age alone.

You might also check your dashpot. Its function is to stop backfiring when you drop your foot off the accelerator by slowing the throttle plate closing...

The other thing is that you might have some lines installed incorrectly causing this noise too....

And lastly, it might be a check valve that's shot... Those orange things on your vacuum lines intended to ensure air only flows one way.

*These are mostly guesses btw. Never heard that sound on my engine, or, well, any engine of any vehicle I've owned before.

RSR

Add pictures btw too. If you've deleted your factory airbox (or even not) it could be the PAIR valve connection too -- folks have described it as popcorn like sound/knocking/etc... It's the one that connects to the top of the factory airbox and then runs to the right side of the engine too.

DrCreosote

Thank you. I'll have a look in the morning. The wife made me go on a trip to the mountains with her, so I haven't had a chance to look at it. I do know some of the vacuum lines were *repaired* by the previous owner. A popcorn/knocking sound describes the way I hear it fairly well, so at least I have somewhere to start.

bbrideau

I could be wrong here but the sound you mention, i have heard it on the wife's 3vz and found out the growl/fart/pop was coming from the intake. take foot off gas and it makes the sound, usually more pronounced if your foot is barely even touching the gas. I noticed it more when i did the ISR mod to it. I know my 22re used to do it before i removed the PAIR system.

DrCreosote

I inspected my vacuum hoses and found two of them that go into a jacket. The previous owner apparently *fixed* them by splicing new to the old, but the old was bad all the way down. Those go to the power steering pump and I'm not sure which goes where, but I hooked them both up and it seems to work fine.

The noise was still there, so I started poking at stuff. I removed some of the vacuum lines and plugged the hole, one at a time, to see if that would cause the noise to stop. What I found was this:



Hose #1 has an orange. . . thing (check valve? dashpot? what is that thing?) and goes down to another device. When I remove that one and cover the hole, it works without making that noise.



The hose is then connected to the EGR valve.

So then I need to know if this is going to cause me to fail my emissions test (California, yay.) or if it is just a noise that won't cause me any harm. I don't mind it being noisy. I can hardly hear it with the hood closed. Also, is it connected to the proper port? I got a vacuum hose diagram and followed it. It's the way the diagram says it should be, but that doesn't mean it's right.

ThanX

Sturmcrow

Excellent photos.

If you pull off the check valve and blow into it, does it seem to act correctly? In other words, does it stop flow in one direction but not the other?

rworegon

This from here should help. Looks like 23285A is what you are after....P/N 90917-10049?

DrCreosote

Took that off and it seems to be working fine. It blocks airflow one way, but allows it the other way. I turned it around just to see what would happen and the noise went away, but I smelled a lot of gasiness in the exhaust.

RSR

That's part of the PAIR system: http://personal.utulsa.edu/~nathan-b...78pulsedse.pdf

In your picture, I think it's backwards.

And this covers all of the vacuum emissions hoses: http://personal.utulsa.edu/~nathan-b...74layoutan.pdf

RSR

Btw, the foam jackets you're referencing I'm pretty sure are standard from factory. Used to hold the hoses together and/or prevent from abrasion.

DrCreosote

If it's backwards in the picture, then it is installed backwards. Thank you, I'll flip it around and consider it mostly fixed. Thank you also for the diagram. I'm not scared of the hoses any more, but it doesn't mean I know where they go.