S3 not boosting properly

[Craig Mel s38p]

Hi guys and girls I'm looking for a bit advice I've recently just fitted brand new plugs Audi R8 coil packs new oil filter fuel filter and a decat pipe but my car seems a bit sluggish now seemed ok when got it back from mates garage but doesn't seem to be boosting as hard now I can hear turbo but feels like maybe a boost pipe has come off I'm off work wed and Friday so was wanna have a good look about it and see what I could see any help would be much appreciated tho thanks Craig