ok this might be a bit long winded but here goes.car is 850 2.5L SE, engine fault light came on a few days ago after i was poking repair on big air hose that goes into inlet manifold, i could hear air being sucked in through the repair, so i guessed that was what caused the light to come on. Today i replaced the hose and read the onboard diagnostics. Placing the jumper into the A2 socket these are the codes it read back to me in this order,113 (long term fuel trim lean), 512 (long term fuel trim too rich) and 231 (long term fuel trim at limits at partial throttle). the first two sound like they are contradicting each other. car has definatly been using too much fuel. trouble is i have read the codes, repaired what i suspect was causing them, but now can't get onboard diagnostics to reset. it says on instructions i have to clear the codes push and hold button for 6 to 7 seconds then release as soon as led comes on, well that would be ok but when i push the button the led comes on straight away, so nothing is being cleared. have read somewhere else about putting the jumper into socket no.7 pressing the button 4 times and then the led should glow continuously etc but this doesn't work either. have also tried reading codes from other sockets, i only have connector in 3 sockets 2,3 and 7, before resetting but this doesn't work either. please help

 

How to read DTCs:
http://volvospeed.com/Repair/a2.html

As far as your specific codes; have you done a full tune up (aka stage 0) first? If not, I would start there, and also ck for vacuum leaks.

BTW: can't tell what you're talking about with regards to your air box; post pics.