2001 LC boost problem

[Shmoo]

hi all. My mates 2001 lc 1.8 t APP has got what I think is a boost issue. when the engine hits 3000 rpm there is a big hick that goes through the whole car. it only lasts for approx half a second then the car goes as normal. sometimes it does a double hick one straight after the other. The fault seems to be intermitant but happens more often than not. the car is remapped but unsure who by as it was already done when purchased. sometimes the dv can be heard hissing when it happens and other times not.

Up to now we have replaced spark plugs, replace n75 valve , n249 bypass, sai bypass, new dump valve, pressure check from turbo outlet to throttle body(ok) and new fuel filter.

we have checked the faults and found bank one prob one no activity and maximum charge pressure surpassed. could it be that it's over boosting causing this big hick? or could it be the lambda sensor causing fault?

we're are at a standstill to we're to look now. the car also has a Jetex filter fitted. the problem was already present before fitting parts and doing bypasses so they don't seem to be the problem. sorry for the long story and and ideas would be greatly appreciated.
thanks jamie