my mk3 gti 8v AGG has started cutting out when i'm declerating

i have just removed the air intake pipe to clean the throttle body to see if that would cure it but it was mint inside?? the intake pipe is split tho and has been taped up by a previous owner, would this cause cutting out?? if not what could it be?? it does it when hot or cold but doesn't do it all the time, its just when changing down gears, dip the clutch and it just cuts out
any help would be much appreciated