Running poorly please help

I have recently brought a g reg golf mk1 gti and it has been running and driving fine a little lumpy but I believe this was because it needed a service , however yesterday morning I tried to start it and it stalled the first 2 times straight away 

So I tried revving it as I did so the revs went down to nearly stalling and gradually picked up but when I let off the throttle it kept making like a poping noise 

Any ideas guys I am clueless 
Thanks

If pumps running then will be to check filters and tank for rust. Debris choking engine. Seems to be common theme. And especially when cars coming out of retirement and hibernation. I ended up strip tank fuel lines filters then to injectors before got running again. 

Ok thanks I have just got all the filters and service parts so I'll change all them first and see how she runs 
It was just strange that it stopped working Overnight 
Are the injectors prone to breaking down do you know 
Cheers

I have changed air, fuel filter and the spark plugs and still have the same problem can anyone help me

What is the thing connected to the fuel pump under the car I have been told it is a fuel accumulor is this correct and could this cause the fault 

Have you looked at the fuel filler neck, shine a torch down it from the filler cap end and look for holes/rust, if dirt and water gets into the fuel system is causes alsorts of problems.
How old are the HT leads, dissy cap and rotor arm? If you are not sure it's worth changing them as well as part of a major service.
There is 2 fuel pumps on theses cars, 1 in the fuel tank (lift pump) and 1 underneath the car (main pump) the accumulator only holds the fuel pressure once the car is switched off so it's easier to start when when hot as the fuel pressure is already there, it won't make any difference to tick over or running.
If you lift the base of the back seat up you will see a black cover, remove this and you will see the top of the fuel tank, start the car and then unplug the connector if the main pump gets noiser and the car struggle to tick over/rev the lift pump is working if not difference your lift pump may be dead. New lift pumps are £25 new.

Thanks for the help mate I will try that out when I get home see how it goes 

I tryed out the lift pump and it was fine I changed a block on the front which I believe was the fuel pump actuator and fixed the problem 
The old one was full of grit prob from the tank