If there are problems in the cat or o2 sensors it may take some days for codes to reappear. Several different fuel related codes could come up as I said without it necessarily being those parts. If you get some, maybe post what they are.

When you say the engine runs rough can you describe this more? If it is rough at idle but otherwise ok then the throttle body may be dirty. On the older 850s this is a purely mechanical part which seems to need cleaning every 2 or 3 years. I don't know what is on your car but if similar you could ask your tech to clean it.

It would be a good idea to inspect vac lines for clogs, looseness, cracks. The ones to the idle air motor (if your car has one) would be suspect, as well as the crankcase vent (PCV or rebreathing lines). Also the bellows that connects the air filter box to the throttle bore. Sometimes one or more of these will separate, crack, or fill up with carbonized gunk. Is your air filter clean enough to let light thru?

If something is wrong in the fuel system the car could be hard to start, emit smoke from exhaust (black smoke) or lack power at highway speeds (could also have rough idle). Fuel filters are often replaced after about 100K miles but this would depend on what the filter experienced. If no dirty gas was ever in the tank the filter might last for ever. If lots of dirt then the filter could clog soon. A good test for the fuel system is to check the fuel pressure with a gauge. If the pressure is too low or fluctuating or too high, then pump could be weak, filter clogged, regulator sticking or injectors or lines leaking. Checking is not a big job.

If the MAF sensor is not right the engine may have many different symptoms. There should usually be a code and it would probably come up right away. The MAF sensor on Volvos I've had is self-cleaning and doesn't require attention. It is a delicate part so shouldn't be opened up or disturbed without reason. If it quits it will usually burn out suddenly and then the car will try to start but won't run at all. The electrical connector on the MAF can get loose or dirty and cause erratic operation of the engine. On some other cars (read Ford) the MAF sensor does get dirty and needs to be cleaned.

good luck