Golf Mk3 ignition knock

[Handsolo]

My 1995 Golf Mk3 GL Auto starts and runs very well - with one exception. If I try to accelerate even moderately quickly from low revs (anything less than about 2000-2500rpm) there is a fairly severe ignition knock (or 'pinking' as we used to call it). This means that while driving it in town I have to (a) drive very gently, and (b) constantly shift to a lower gear to keep the revs up. The Haynes manual shows a Knock Sensor bolted to the engine block but I can't see anything resembling their illustration, and my local VW parts department tell me that my car is not fitted with one. Is this likely to be curable by some sort of adjustment or am I looking at a replacement ECU (or something)?

(incidentally, is VAGCOM simply a diagnostic tool, or does it enable some settings to be changed via the PC?)