84 240 DL wagon start then die then no start

my mom's 84 240DL wagon is having problems, the fuel mixture is too rich so the plugs fouled out, so she had me replace em, and it started right up and ran good for about 5 mins, then died and will not start up again, i pulled out one plug and looked at it (brand new plug) and it was kinda dirty and smelled like gas. i dotn really know anything about Volvo's at all, so what should i do? is it bad fuel injectors? or what?

Replace the O2 Air mass flow sensor. It sounds like it has gone bad because the mixture is so fuel rich. It controls the air fuel mixture.