The 2.5 turbo cars are notorious for this problem, low power usually caused by one of the many pneumatic relays, sensing a condition to compell the computer to be in the limp home mode, no boost, sometimes its the main computer though rare, there is a 12 page test procedure in the manual, I would suggest if you are not familiar to take it to a good mechanic and have him pull the codes. Then you can decide if you want to replace the relays on your own, then again if the guy is good I would just let him do it, the relays are not that expensive and troubleshooting can be madding.
Good luck
Ron