Saab 93 2007. sounds dreadful

Hi i have a saab 93 2007 its a 1.9tid
The car takes 2/3 attempts to start
When started really struggles to find power
(sounds like its about to stall)
When u start to drive i put foot on accelerator and
loads of white smoke out of the exhaust thr revs
only hit half way like its not getting power.  Then
the revs will kick right up and im away.
But then driving i can feel the loss of power every
couple of seconds.
Theres a horrible rattle too (not sure if this is same
problem)
Ive checked egr, mass airflow and pipes going into
injectors and they all seem fine.

Any help please