Mk 1 gti cabriolet 89/90 breather pipes

I'm hoping someone can help! Trying to find a complete set of breather pipes , my engine is hunting on idle and I think there's a leak in there somewhere!

Nomenclature is a wonderful thing.
Over on this side of the pond we call them Vacuum hoses.

I see a venturi pipe that is normally over here only on Automatic Transmision equipped Cars.  That is the Gray Hard  "Y" Pipe.  

I see a couple of things that I would eliminate.
A few things to be aware of.

But test things first.  I would spray brake-kleen or Carb-cleaner on all connections and hoses as that is where they leak.  You an also take it in and have it smoke tested as that is the Definitive way to test for vacuum leaks.

The Venturi or Suction pipe has 2 parts, the Black piece, and the Gray Piece.  In between the 2 of there there is a o-ring that can crack . Take great care when working on the thing especially around the Yellow (hard to get new one) check valve.  Separate the thing and see if the o-ring is wonky.

Not Circled is the Idle by-pass screw on the back side of the Throttle Body.  If that screw is easily turned by hand, then that is a bad O-Ring, and a cause of fluctuating idle.
Count the turns (7mm open wrench on nut) it takes to remove it, write that number down.  Replace the o-ring, and wrap the threads and threads of that screw with WhiteTeflon Plumbers tape, threads only. return to value you wrote down.

Second I see a Jubliee or Screw clamp on one of the connections.  On smaller diameter hoses they tend to tighten down the hose elliptically and not Circumfrentially.  

I have seen the smaller diameter Jubliee clamps pucker the hoses, and Cut the hoses so I never use them on less than 1 1/2 inch diameter hoses of any type.



Secondly check the TB to Fuel distributor expansion connections as I have seen cracks occur on them as well.  

Any and all unmetered air is a NO-NO, and Vacuum leaks are a weakness of the VW's and can occur anywhere, don't discount any and all Vacuum lines.

Thanks for your comprehensive answer!