Check engine light code .

 

plenty of info online - just google Volvo P0026 and you'll see references to the VVT solenoid and the VVT gear (cam actuator). Since the system is driven by oil pressure the first thing to do is change the oil and use a premium synthetic oil of the correct weight for the car, clear the code and see if it returns. A more agressive approach recommended by some is to do a Seafoam treatment to see if it removes any of the tarnish on the VVT gear or you need to replace the solenoid then possibly the actuator. Plenty of vids on Youtube as well.