Dealerships are in the business of replacing components one by one, at your expense, until the dreaded CEL goes off.

Probably there was nothing wrong with MAF, and you're out of $300. Most likely the front O2 sensor is bad, maybe the cat converter is bad, but first the dealer makes you pay good money before they say is the cat converter. Get the codes from the dealer.

Stop patronizing that dealership and find yourself a trusty indie volvo repair shop.

If you're handy with tools and don't mind getting dirty, you could replace the O2 sensor yourself, they run about $150 so you'll save a bundle in labor.
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'88 240, '92 745, '98 v70 -John, Tampa Bay