I've had some troubles with my volvo 850 wagon (same as v70 essentially). There are some issues with these cars that even the volvo gurus cant explain. I had a no-start issue that was only fixed by disconnecting the turbo lines and starting the car naturally aspirated, then reconnecting the turbo. No one can explain why, its just what works with these swede machines sometimes. I dont think this is going to help you since you are actually running... just rough.
Check the intercooler. Mounted infront of your radiator with a line from the turbo and another to the intake manifold. With high miles these become oil reservoirs for blow by oil. Fill it with enough blow by and you will choke the air. If it hasnt been dragged on the ground too much (my high driveway entrance has gradually sanded my intercooler flat) there is a brass, or aluminum fitting there to remove and drain it. The design of that intercooler is terrible, with its plastic bottom and being mounted 3inches from the ground. I have a spare in my garage for the day i finally rip the whole thing off.
Another spot to check is the coil. Mine went bad in bursts, which would leave you with symptoms like you say. Im not sure if they went to packs on the V70, but my 850 has a coil and distributor.
if you cant find any more volvo guys here there are a couple sites you should check. for parts www.ipdusa.com
is the only place you should ever go to find parts, OEM and aftermarket. And a volvo forum thats full of enthusiasts that i would say are into volvos as the people here are into 2 wheeled adventures : www.matthewsvolvosite.com