Unless you have what it takes to fix it I recommend you have it towed to a reputable Volvo repair shop and pay them to do what they do, diagnose and fix cars. Because of the intermittant nature of your problem I suggest you advise them of this and be prepared to leave the car for several days. Otherwise it could be a faulty fuel pump, pump relay, cam position sensor (not likely), engine speed sensor, or possibly a mass air flow sensor. If I had to take a guess at it I'd say a mass air flow sensor aka the MAF. You should have a blink box on that car that will allow you to pull codes out of the control units to see if it has stored anything, past that you almost need to have a few "known good units" on hand to swap out and see if it fixes it. There in lies the beauty of paying someone else to diagnose and fix it, sure they will charge you money to do it but they have to stand behind their repair. You pay them what they want to diagnose and repair your vehicle and it is then their baby. When it goes belly up again because they did not fix it right the first time then you can tow it back to them and politely let them know that it is not fixed as you paid them for and that they can either fix it for free now or go ahead and reinstall your old parts for free, reimburse your money spent, and then start from square one again. The shop will do one of two things, either step right up and take care of you (the right thing to do) or spin the story and tell you that while they might not have fixed the car completely, it still needed doing because there was more than one reason why your car was cutting out and because of the intermittant nature of the problem they only got one part of it fixed and that you will need to pay some more for them to find "the rest" of the problem and fix it at an additional cost to you, B.S.

Mark