I have a 320d E46 and it is loosing power but the turbo has just been reconditioned what will be the cause?

https://www.newtis.info/tisv2/a/en/e46-320d-lim/repair-manuals/11-engine/11-28-drive-belt-with-tensioning-deflecting-element/BzRYhMS at the bottom of the page

Don't worry I'm sure you will get the solution of your problem, just check the link I attach
https://www.reliable-store.com/products/2001-bmw-320d-330d-e46-car-service-manual-spanish

thermostat is stuck. change it
also check the viscous fan

find a new mech.?

make sure the distributor is firing on number 1 cylinder then determine tdc of number 1

Sticking egr valves causing black smoke . Front wishbones and rear coil springs are common

if you go to the dealer they will copy the mech manule it you ask them as they want you to get frustrated and take it to them
so go on and ask and if all else fails take it to them or goto local parts store like auto zone they can preint it off too
dealer is best bet though

replace fuel presure regulator

take off turbo hose blowing into intake cheqe for pressure