Random Spluttering - VW Mk2 Golf GTI 8v

I own an 1990 8 valve 3 door Golf GTI

The problem:
Every now and then the car splutters, e.g loss of power sometimes bring it to a stop where it eventually cuts out. I can restart the car straight away and the pattern repeats. After a period of a few minutes the fault disappears and the car will run like a dream.

The History:
This seems to be happening more frequently just of late, when it's damp and cold. However I've driven the car to Italy and France in past years where it's happened in very dry hot conditions.

Condition of the car:
The car is standard and done approx 168k miles the engine is serviced every 6000 miles, I've had the plugs and HT leads changed and it's rolling-road tuned. I can never re-create the fault for the mechanics who think I'm :screwy:

Does anyone have any ideas what this might be or an idea of how to isolate the fault. At the moment it's like :banghead: .

Thanks

TEX102