Hi, Sounds like the wastgate control is stuck, when the engine is cold
see if you can move the wastegate linkage with the actuator rod,
you should be able to feel it move and spring back aginst your movement.
sounds like its stuck open,, actuator or wastegate, you may also have a weak boost pipe letting out air,
check all hose's to and from the turbo inc the intercooler and to the inlet
manifold, if a vacuum leak is present Rs turbo mfi, usually run rough or cut out on idle.

Regards Dave R.