What is this part

Not long owned my mk1 golf GTi 1983…… found this in the engine bay seems one of the pipes is blocked off with a screw I'm guessing to hold pressure? Can anyone tell me what this is why there's a screw shoved in the end and if / how do i replace this and put it right……

Also could this be the reason my car won't start first time when engine is warm/  after a short drive 

That is a vacuum line.
On my 83 GTi, I only have one line coming off - the other is blanked off.
The one that does come off goes back and through the bulkhead to the cluster to drive the fuel consumption gauge, and MFA.
On the back of the throttle body is another vac line that runs to the dizzy advance.
What my 83 does not have is that plug and connector on the throttle body. That would suggest - if it is a UK car and original engine - that it has been modified.

The hot start issue could be a lack of residual fuel pressure which can be caused by:
- a failed fuel accumulator (located under the car, near the tank - it's a metal cylinder with 2 fuel lines coming off it) or,
- bad non-return valve on the fuel pump
Only way to know for sure is to get a fuel pressure test gauge and go through the tests - plenty of posts on how to do that.

paceman said

That is a vacuum line.
On my 83 GTi, I only have one line coming off - the other is blanked off.
The one that does come off goes back and through the bulkhead to the cluster to drive the fuel consumption gauge, and MFA.
On the back of the throttle body is another vac line that runs to the dizzy advance.
What my 83 does not have is that plug and connector on the throttle body. That would suggest - if it is a UK car and original engine - that it has been modified.

The hot start issue could be a lack of residual fuel pressure which can be caused by:
- a failed fuel accumulator (located under the car, near the tank - it's a metal cylinder with 2 fuel lines coming off it) or,
- bad non-return valve on the fuel pump
Only way to know for sure is to get a fuel pressure test gauge and go through the tests - plenty of posts on how to do that.

paceman said

That is a vacuum line.
On my 83 GTi, I only have one line coming off - the other is blanked off.
The one that does come off goes back and through the bulkhead to the cluster to drive the fuel consumption gauge, and MFA.
On the back of the throttle body is another vac line that runs to the dizzy advance.
What my 83 does not have is that plug and connector on the throttle body. That would suggest - if it is a UK car and original engine - that it has been modified.

The hot start issue could be a lack of residual fuel pressure which can be caused by:
- a failed fuel accumulator (located under the car, near the tank - it's a metal cylinder with 2 fuel lines coming off it) or,
- bad non-return valve on the fuel pump
Only way to know for sure is to get a fuel pressure test gauge and go through the tests - plenty of posts on how to do that.

Brilliant thanks for your help! I know about the modifications in the car…. I think this is because this isn't the cars original engine and hasn't been replaced properly!

Could this be the reason the fuel level gauge/indicator doesn't work? 

Thanks for your help!

Does the water temp gauge work?

Otherwise, I would bet on a broken wire or corroded solder connection on the Potentiometer in the tank.

Take your sender connection off and run a 9Vdc battery from the Positive to the violet wire, and ground n the brown, if the meter goes 3/4 to full, then you are good on the wires and meter, and need to concentrate on the sender.  In the archive I have a how to do that click the link to my how to's on my signature go to the electrical ones.

IF the meter doesn't deflect then look at you wiring to the cluster and ring it back to your sender.  If the wires on the connector on the cluster doesn't ring or 0 OHMS then you are looking at your wiring to the meter.

If that rings, then look at your cluster.