Clio 1.2 2001 steering problem

[Scattle]

Afternoon guys,
My brother has a mk2 2001 Clio, 1.2 Dynamique.
He had a low speed crash in it recently and bent the front subframe. He got a garage to replace the subframe etc.
He has since had the car back, and the car does not self-centre and the steering feels stiff/heavy one minute and goes very light the next.
The car did not do this before he crashed.
What could be causing this?
Thanks in advance.
Steve

 

[RenMatt]

Did the steering rack get replaced ? it isn't uncommon for the rack middle shaft to bend on hard impact, this can be detected if it is easy to turn one way but feels harder to turn back if you get what I mean . Also the rack sensor can give problems .