First welcome. It is not an easy situation to point to a specific item, but a global thought is that the mechanic who worked on your car may not be the best choice. If possible ask members here for a known Volvo specialist in your area, or perhaps try using local.google.com to search a garage that w...

Original MAF (mass air flow sensor)? Ever cleaned?

I'd google/read up on replacing your MAF and the symptoms of one going bad. If this is the issue, cleaning the sensor, or replacing with a junkyard one with the same PN would keep your expenses down.

Good luck.