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Discussion Starter · #1 ·
I was pulling the vacuum line off to remove the plenum the other day to change my spark plugs and the whole plastic vacuum line on the "power valve" broke off. I've noticed ZERO ill effects of this while driving (though the new one will be here today, luckily only a $40 part).

So i'm wondering, what exactly does it do?
 

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I was pulling the vacuum line off to remove the plenum the other day to change my spark plugs and the whole plastic vacuum line on the "power valve" broke off. I've noticed ZERO ill effects of this while driving (though the new one will be here today, luckily only a $40 part).

So i'm wondering, what exactly does it do?
I think its like a pre-throttle butterfly. As you load the engine that opens and gives the engine more air based on system vacuum. If its not connected it probably stays closed all the time, which is probably fine for around town, and gives better economy. But of you are towing or need to floor it to get on an on ramp it will stay closed. If you dont fix it, id say pull it out.
 

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Discussion Starter · #3 ·
Possibly

I think its like a pre-throttle butterfly. As you load the engine that opens and gives the engine more air based on system vacuum. If its not connected it probably stays closed all the time, which is probably fine for around town, and gives better economy. But of you are towing or need to floor it to get on an on ramp it will stay closed. If you dont fix it, id say pull it out.
I"m fixing it. it's a $40 part. I don't think you can just pull it out, it would leave a giant hole in the plenum.

But, the only vacuum lines are coming from the plenum, so that can't be right i don't think, because it would only be putting air back in that was already in the system.

Also, you can't put NON MAF'ed air into the system because your A/F ratio would be lean. which is dangerous.
 

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Discussion Starter · #4 ·
Right

I think its like a pre-throttle butterfly. As you load the engine that opens and gives the engine more air based on system vacuum. If its not connected it probably stays closed all the time, which is probably fine for around town, and gives better economy. But of you are towing or need to floor it to get on an on ramp it will stay closed. If you dont fix it, id say pull it out.

You were right to some point. IT is some sort of butterfly valve. I'm not sure how it works sense the air is coming from the manifold. My buddy who works at nissan said on previous years it shortened and lengthened the intake runners to be optimal for RPM. I'll post a picture of it when I get back home.
 

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They had that same kind of idea on my 01 qx4...except mine were on the lower intake plenum and we're known to have the screws come loose and ruin your engine...glad to see they updated it...kinda

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