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Discussion Starter · #1 · (Edited)
Have been trying to sort out my boost issues and have found that a tube running from the black plastic Bosch vacuum valve thing that sits off the side of the large rubber inlet tube going to the turbo (best description I can give), was loose where it joined the throttle body. I was able to just pull this connection out by hand very easily. The hole it goes into, and the loose tube can be seen in the photo.

What does this tube do, and how is it meant to be sealed into the hole that it goes into in the throttle body?

I also found that the small diameter vacuum line running from the black plastic Bosch valve to the inlet manifold was split where it joined the small plastic connector at the manifold. I replaced this, but still not really sure what it does. I guess fixing all these little things I see is the first step to solving my long running issue.
 

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The thing you are describing is the turbo bypass valve - it's a recirculation valve that opens under vacuum (when you shut off the throttle to change gears) to allow boosted air to flow to back in front of the turbo (the rubber 45 degree coupling in front of the turbo). It does this to give the air somewhere to go when the throttle plate is closed, otherwise air bouncing off the throttle plate will slow down the turbo/stall the impeller.

It's like a blow off valve but instead of to atmosphere it sends it back in front of the turbo, theoretically improving spool up time between gear changes.

the thin vacuum line that was split controls the opening of the valve when you shut off the throttle, if that's split that would create a vacuum leak. The loose fitting on the throttle body would also create a vacuum leak.

These could well be related to your boost issues (leaning out), let us know :)
 

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Discussion Starter · #3 ·
Thanks for the info. It'd be nice if this helped my issues a bit.

I have replaced the thin split tube, and have cleaned the mating surfaces of the throttle body and the hollow metal cylinder that sticks into it that the rubber tube gets hose clamped to. But how is this metal fitting meant to stick in the throttle body? Was it a press fit from the factory that has somehow come loose, or should it be glued or something?
 

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Oh sorry I misunderstood, I didn't realise the fitting had broken free. I think it's just glued in there with a certain high temp glue. You could use a fuel proof epoxy, or something like quiksteel/jbweld to secure it.

I'd pull the Throttle body off to do this job, you don't want bits of glue/jbweld etc getting into your engine.
 

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If the tube still has a fairly snug fit but is loose, Loctite does a good job of securing the tube.
Loctite doesn't hold up to heat although the intake shouldn't get too hot...

The factory fix is a thin smear of jbweld. No need to remove the intake.
 

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Loctite doesn't hold up to heat although the intake shouldn't get too hot...

The factory fix is a thin smear of jbweld. No need to remove the intake.
Erm yes it does. It's retains it's bond well into 150deg Celsius (losing strength as it gets hotter) you use 250deg celsius + to break it away when disassembling, it's used in gearboxes which have 80-100deg Celsius oil in them for hundreds of thousands of hours, trust me the loctite is still on there when you spin the nuts after removing the stakes.

In saying that I would go with an epoxy because they're cheaper unless you have loctite lying around, to say that loctite wouldn't work however is probably incorrect. The TB probably doesn't get much over 60-70 Celsius.
 

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Throttle body can potentially be at over 100deg c...........engine coolant runs through the throttle body side water jacket....
If any sealant is to be temperature qualified, I would be looking for something 200deg c......get some "headroom" in the working capacity of the joint again.
 
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