If you're serious about the car, take it to a dealer or an indy with VIDA-DICE and have it scanned (you could take it to an Autozone and have them read the generic codes if you don't have your own scanner, but you won't get the proprietary Volvo codes).

The one relatively expensive thing to check out is the electronic throttle module (ETM). If it goes south (and eventually they all do), you'll be looking at $500 to fix it. Check and see if it is original (white label) or updated (yellow label). Consensus seems to be that Xemodex is the way to go if it needs replacing.

Good luck!