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Discussion Starter · #1 ·
A couple of issues. I'm reading about -10 psi at idle and it used to be around -18 I believe. I also can't boost more than around 12 psi. Had the PCV breather hose go on me a few days ago, so replaced that, thought it might fix my vacuum leak, but it didn't. I had a vacuum line had a crack in it awhile back, and repaired that with new hose. Would a backwards installed check valve cause this headache? Which way is it supposed to go?

When I had the air box off, I noticed the pipe between the MAF and the turbo was loose. I had never noticed this before, I imagine it should be tight? How in the world do you tighten that up and how do you get at that pipe? There were some lines coming out of there, I think one vacuum line for sure. I couldn't see any clamp or anything to tighten it on the turbo.

Please bear with me and my ignorance with some of these systems- I'm trying to understand how the vacuum system works as well as the PCV and haven't fully caught on yet. :rolleyes:
 

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Yes the hose that goes from the MAF to the turbo inlet should be clamped on with a clamp.

It's a bit of a PITA to get to, but it does need to be on there good so it doesn't suck in unfiltered air.
 

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Discussion Starter · #3 ·
That wouldn't cause a boost or vacuum leak though would it? Since it's before the turbo?

Sent from my Q10 using Tapatalk
 

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If your idle vacuum is -10inHg (it's not psi) and you're not getting full boost then there probably is a leak post turbo. So check every pipe, hose etc that is somehow connected to the intake. Post MAF pre turbo inliet pipe should be tight too. But it wouldn't cause low boost nor insufficent vacuum during idle.
 

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Discussion Starter · #5 ·
To clarify, there isn't a chance this is being caused by a backwards check valve on a vac line is there? I'm not sure which way these things go. I think I put it back the way it was, but there is the chance I didn't, also.
 

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Dont know which check valve are you talking about, but reverse it and see if it makes any difference
 

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You need to replace all the vac lines at this age if that has not been done already. Also replace the tcv with a new oem unit while in there. And get that pipe tight on the turbo definitely should not be loose or hanging off. It's a pita to get your arm down there but I have done it many times. Also you need to boost leak test your car the right way like in the pic below. It will show you some crazy stuff that you would never guess.



From my electronic gismo- Galaxy S6
 

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Discussion Starter · #8 ·
I am thinking about replacing my vacuum lines. Where do I order? Also does a boost leak = vacuum leak as well or vice versa? What's this with the TCV? I think my turbo is ok.
 

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Once all vac lines are replaced correctly you won't have any vacuum leaks. The tcv is the turbo control valve. They are a common failing item on these cars. It's mounted on the side of the air box and has 3 vac lines running into it. When I replaced my lines I ordered the blue silicone vac hosing from viva and just cut the hosing to sections of what I needed.

From my electronic gismo- Galaxy S6
 

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My gauge reads -10 average all the time at idle.
 

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My gauge reads -10 average all the time at idle.
Definitely should be more. Mine says about -20

From my electronic gismo- Galaxy S6
 

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Depends on altitude too, at sea level I idle at about -20 inHg, but up here above a mile its closer to 12.

Even if the intake pipe or other intake plumbing has issues, the manifold vacuum is completely dependent on the integrity of the intake manifold gaskets and throttle body, so leaks before that should not effect your idle vacuum. Even if you have a leak, the throttle should close up some to maintain the correct RPM even if the PCV or EVAP systems have leaks or issues.
 

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I do get more than -10 sometimes, i saw -15 this afternoon.
 

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Discussion Starter · #14 ·
Can someone specify the correct part number for TCV? I looked it up in VIDA, and there are 3. PN 30670448 says EXC B5254T4 so I'm guessing not that one, but that leaves me with 9473212 or 30670449.
 

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What does it say next to these other part numbers? Is the a text like < CH xxxxxx or smth?
 

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If your idle vacuum is -10inHg (it's not psi) and you're not getting full boost then there probably is a leak post turbo. So check every pipe, hose etc that is somehow connected to the intake. Post MAF pre turbo inliet pipe should be tight too. But it wouldn't cause low boost nor insufficent vacuum during idle.
If you had a boost leak preturbo, what would the symptoms be? My intake pipe is loose on my turbo.
 
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