1990 Golf 1.8 16v GTI Engine Vacuum?

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Hi all,

Im new to the forum and was wondering if anyone could help me with a problem I'm having with my 1990 MK2 Golf 16v GTI with the KR engine?

I've not had it long and was having trouble with the engine idle being all over the place at different engine temperatuers. After taking a look under the bonnet, I noticed a quite loud hissing sound coming from a hole in the unit on the right hand side of the cylinder head (looking from the front of the car) where the fuel pipes run to, from the unit on top of the air filter housing.

When I cover the hole with my finger whilst the engine is running, the revs instantly drop to a normal sort of level (instead of being slightly irratic).

I have looked to see if I can find a vac pipe that has come off, but can't find anything. I also noticed that when the hole is covered, no hissing can be heard from anywhere else, as I would imagine that if it should be running off somewhere else, the other end must be disconnected too and would also be hissing?

I was just wondering if anyone could tell me what should be on there, or maybe if you have one of these cars yourself, have a quick look to see whats missing.

Ive attached a couple of pics just to let you see exactly what I am talking about, it is the hole next to the blue electrical plug.

Thank you in advance for any help anyone can give me, I have only owned 8v GTI's up to now and so have a limited knowlege of the 16v engine and so any advice will be much appreciated.

Russ