Hesitation at full throttle (1990 Audi 200 MC-1)

[Gerard]

Hi!

Car in question is a 1990 Audi 200 with MC-1 engine.

At 4000rpm, under full throttle, the car cuts outs rapidly in succession, 
plenty of hesitation. However, gently applying the throttle will make it go 
smoothly to 6000rpm without the cutting out.

Any clues on what needs checking under such conditions will be much 
appreciated. Throttle switch perhaps, or maybe some other sensor? Clogged 
fuel filter maybe?

Thanks. :)

G.