without meaning any offence to your mate or anything but just as a precaution i'd get all four of those injectors pulled and the injector seals replaced
DONT get the seal kits from VW, they cost a small fortune from them, get them from Andrew Page i picked mine up for about 6quid per set
get the seals replaced on each of the injectors, get the injectors reseated
then ensure all the injectors are realigned in the cylinder head and all the plugs are connector, replace the valve cover
make sure all the pipes etc are connected, just because one of the injector connectors wasnt connected doesnt mean pipes should start flying off! you've probably still got a boost pipe loose somewhere hence the loss of power!
get under the car and start looking for missing clips around hoses
good luck!