There's no way for us to give any guesses based on such limited information. Because you have exhaust fumes in the car, take the car to another mechanic and have it fixed ASAP. For all we know there's a hole in the exhaust pipe and a cabin leak. A vacuum pump and VNT actuator won't cause exhaust fumes but it could cause low power.
Here's a checklist for diagnosis low power:http://www.myturbodiesel.com/1000q/multi/low-power-fix-TDI.htm
Here's a checklist for diagnosis low power:http://www.myturbodiesel.com/1000q/multi/low-power-fix-TDI.htm
