s.turbos

hi new on here im looking for any help! i have a 02 lupo gti it has ran great for 2 years never any bother started to burn oil valve seals so had engine out head off sent away for skim new oil seals i have put new piston rings new shells also. rebuilt engine new timing kit water pump new clutch ht leads plugs so on and now after fitting it runs very rough!! like its running on 3 everything looked at no vac leaks it keeps saying the manifold pressure sensor got a new one today that was a genuine map sensor also no change still got that g71 code all wiring good any help please??