ASV fault?

Hi guys

Having a few niggles with my polo gt

Its got the BLT engine, garret 1752 turbo,fmic de cat and full system, John has been mapping it brill, but it developed a hesitation / splutter when under WOT from low revs, Johns checked and mapping is spit on as even plays up with standard mapping, if I'm slow and apply throttle gently its fine, I've tried a new vac box, checked the actuator and holds vaccume and opens correct, I've ran with maf un plugged and no difference, egr valve is removed and mapped out, only thing I can think is the asv valve, but I there any vcds test?

Thnks

Dan