I had the same issue a few weeks ago after getting my first tune after mods, if you have a compressor handy wind it down to 12psi, ram that in its guts and see if it opens, next thing to be (and this is more easy if you pull the turbo off) you wanna check the preload of the actuator, to do this, fix the actuator to the turbo, while holding the wastegate closed, wind the arm untill you can freely put the actuator arm onto the flapper, next wind the arm in 3 complete turns then grab a pair of pilars and pull it onto the flapper and secure with c-clip, the next thing I did was I remover all intercooler piping and sprayed hair spray, just a little up to the joins, (acts as a sealer), refit all pipe work and make sure all clamps are tight, leave 24hours to insure that hairspray drys and seals correctly, next check all vaccume lines for splits, kinks, and if you can secure with hair spray and cable ties, make sure bov is not stuck open, compare with known good one, after that you should be ok, other wise I'd be looking at the turbo or tune, I'm pretty new to the whole modifying of these engines but that where I'd start, good luck