Hi Guys, I recently purchased '94 Golf & I've been test driving it to try & detect early what issues it may have. I'm very much a novice with cars (changing the oil's as technical as I get) but I have patience & time so any advice you give me I'll try to put to good use.
Anyway, I've experienced the following issue & I'd like some advice on how I can sort it out! The symptoms are as follows:
When driving at speeds at and in excess of 140 KPH whilst at revolutions at and in excess of 3,200 RPM, the engine will cease to produce accelerating power and will begin to slowly lose revolutions. When one backs off the accelerator, and then reapplies it, the power will often come back on in full until the issue re-occurs (usually within 10 seconds). In this way one can accelerate up-to and through 180 KPH, but in doing so one will experience the above symptoms on multiple occasions. The symptoms do not occur when one simply revs the engine hard in lower gears e.g. taking 1st or 2nd gears through to 4,000+ RPM. However, no sustained RPM test were made using lower gears, so it’s possible that if one were to sustain the engine at high revolutions in low gears that the issue would be replicated.
Disclaimer: I'm an Aussie, but I live in Germany. The above test(s) were conducted in the unrestricted section of a quiet autobahn (the old road between Cologne & Bonn). 
I'd say the most likely culprit is a dirty fuel filter.
Awesome, thanks Jim, that's what I was hoping it'd be. What sort of time frame is needed to put in a new one?
(Sadly, I'll not be able to look into it for a little while though - I purchased a Haynes manual on ebay.de weeks ago, but the only thing I've received thus far is an email saying there'd be a delay of unknown duration...)
Can't say as my avatar is my VW IDI. I have a Racor filter, which takes about 2 min to change.
You should be looking at about 30 mins tops....shouldnt take more than that. If you do it....dont forget to fill the new filter with diesel.
You can fill it with ATF as well, it might be easier to get ahold of then diesel.