A Volvo PO172 code may mean that one or more of the following has happened:
The MAF (Mass Air Flow) Sensor is dirty or faulty.
Note: The use of “oiled” air filters can cause the MAF to become dirty if the filter is over-oiled.
There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
There could be a vacuum leak.
There could be a fuel pressure or delivery problem.