Lack of power after turbo change

[bag320]

Hi,

i have changed my turbo on my a6 avant estate 1.8 t petrol. the old one blew its seals so i got a second hand one of a car that had done 80000 miles and changed them over, my problem is a lack of power. I have run the car so all the oil is out of the exhust and i have run cataclean through so has anyone got any ideas of why i would have lack of power.

Thanks for your time and help