zafira 2.0 dti on a 52 plate poor running?

hi i have a vauxhall zarira 2.0 dti & cant fined the problem with it. no codes are present & car starts fine but onece the car is at running temp it then sounds knockie plus poor power at low revs lots of work done
injectors
injector seals
full service
crank senser
maf
all inlet ports been cleaned
timeing cheqed
vac pipes all changed
leak off pipes plus T all changed