'98 S70 T5 in question.
When it gets down to around -20 to -30C, even with the block heater plugged in for 2 hours, it starts up just fine but but occasionally just won't accelerate. It'll go 35km/h, sometimes even 60. Less than you expect from 236hp. You can let the coolant temp reach normal and drive it for 20km and it won't help. Once it's up to temp, you kill the engine and wait a couple of minutes, start it up again and works like a charm. It doesn't do this regularily, but seems to do it at warmer temperatures than before. First time it was at -35, about 5 years back, yesterday it did it at a little over -20. Humidity might, of course, be the crucial factor, but haven't really checked that.

It has the classic symptoms of carburetor icing, so i started thinking if it could be icing in the intercooler or turbo. Our naturally aspirated V70 never does this. I've used de-icer in the fuel but i really don't think it's in the fuel system, since it runs smoothly and doesn't have any symptoms of a lean mixture, just MAJOR lack of power. If it's ice a hot intake air valve would cure it, but there isn't one on this model, although i understand there is on some.

Any experiences of the sorts?

 

Just a hunch, but the cold air could be messing with your air mass meter.