Had same problem with my 96 850. Local mech cleaned up the MAF and its done well since (3 winters). I'm holding my breath for the eventual failure, but it was $250 I didn't have to spend at the time.
As for plugs ,buy the Volvo branded. The same mech is up the street from a Volvo stealer and has found that nothing else works right in the turbo flying bricks from Stockholm.
Illegitemi non-corundum est.
Tmaximusv screwed with this post 12-01-2012 at 08:59 AM
Reason: More info to response