[Biturbos4] timining belt replaced - now lost power

[bernd]

 i needed a new clutch and with 90000 miles the shop replaced the timing 
belt to.

 they also replaced the auxiliary water pump.
 so now the car lost some power or at least it feels that way (can't get 
the traction control kick in on wet road).

 is there any thing they could have done wrong.

 the engine runs smooth and no check lights are on.

 bernd 2001 s4 avant