P0108 Volvo - v40 2001

Question

Hello, car is running ok when slowly and quite use it in a city, but on a highway, when I try to go fast - appear a smoke from exhaust pipe and engine speed fluctuate (but any way - car speedy).
had on clock:
- check engine and Service Engine Soon Warning Light
- also very high use of gas.

thank you

with respect Aleksandr