996 TT air leak back into intake manifold

Hiya, Been trying to narrow down the cause of my catastrophic vacuum / boost leak, managed to find the fuel pressure reg vac hose had popped off, so sorted that and now the car runs so so much better. Tested again (with the air box off), i could hear a fairly big leak coming back down the unpressurised intake manifold, the big oval shaped one aluminium (yes i'm a brit ) one running down the left hand side of the engine (motor) so I reached in expecting it to be leaking diverter valves, but no. Plus I had tested the vacuum side of the diverters earlier and they held fine. Reached into the inlet further and there is another inlet into the manifold about the diameter of my small finger, probably another four inches further back from the diverters intake and coming from the centre of the car, and i don't know what connects to this, therefore i'm stuck. So the leak is coming into this inlet manifold from the hole slightly further in and i don't know what feeds that I've been over all the parts diagrams i can find and the one that shows the intake manifold, sadly shows the wrong side of it, and does't show the hole where the diverter valves connect, or this other connection. I've been over the other diagrams and again, i just can't find what's feeding this. It's no show on the vac circuit, breather circuit etc, that i can see. Hope anyone who's pulled this apart and knows can help!!! Thanks in advance J

You may have better luck in the Turbo specific forum: https://rennlist.com/forums/turbo-te...sion-areas-50/ That said I had the engine out in my Turbo last summer. I believe the connection you are speaking of is the vent for the oil tank. I have found that if you pressurize the system at the output side of the turbos you get a better read on intake tightness. If you pressurize the inlet side (which is what the service manual says) then air leaks through the vent on the LH turbo (almost said driver's side ), through the oil tank, and out from either the throttle body or the oil tank vent. The oil tank is vented into the plenum on the engine side of the throttle body, too. I have some pictures of the engine out & partially dismantled around here somewhere. There, this pic I saved from an Ebay auction. You can see the rubber hose linking the top left corner of the oil tanks with the intake plenum.

Firstly thank you Theprf, To be honest i think you've nailed the answer, i'll double check on the turbo forum, but i think it's the oil breather, that photo shows the pipe going into the intake manifold casting at about the right spot from my digital investigations The fittings i've put together out of water pipe and caps don't quite fit (too narrow diameter) into the outlet flexi hose after the hard hose coming from the turbo. I guess, bunging up the intake manifold would allow pressurisation, however it wouldn't allow you to make sure all of the one way valves are good. As an aside, i did get a gurgling upon stopping the car last time i drove it, coolant all looked normal, but that sounded like it was coming from the oil tank breather, never heard it before. Cheers J