My car is stalling. What can I do to fix it?

And the correct answer to my question was "Take it to TWO mechanics." The first said, "Well, it's an older car...there could be any number of things wrong with it." I asked him to run a diagnostic, and apparently, he didn't have the correct equipment. GReeeeaat... So I took it to the dealer. Good thing. They found my thermostat was stuck open, and replaced an ECT sensor. They also put coolant in it. The total was $240. (OUCH!) They did replace a flange nut and rubber cushion free of charge, as both were in recall 140 from Volvo. All in all, and expensive trip to the mechanic(s), but I do feel much safer now. CarGrr