On the basis of what you've said there Luke, i'd plump for dirty injectors. As you've got a half-decent run tomorrow, chuck some injector cleaner in the tank before you leave.
If you haven't but just happen to have some ATF-U around, if you have a full tank, add 50ml (that's a pub double measure of spirits so not a lot at all!) to the tank, if it's half a tank, just add 25ml.
If you're going to brim the tank, add the 50ml just before filling up.
Then check the colours on your plugs when you get back.
Certainly the right plugs/gap etc, i don't know who makes the plugs for Volvo but i suspect it's Bosch and it could come from one of their South American plants where stuff has a less than satisfactory reputation. I can't remember which plant it is (Mexico i think but not sure) and Bosch have more than one S American plant but
when you're paying a lot extra for a Volvo branded plug over what an NGK is, i'd stick with the NGK personally.
With the camber mod, check your strut tops on the inner wing, you may have an alternative set of holes you can fit the tops to. For now, until you finish the suspension it would save scrubbing out tyres so quickly. I know it's not your preferred solution but would surely be better than new tyres every few months?
What sort of car has your missus got Luke? Also what did it fail on?
