Ecm 260 is a fuel trim code. and a defective maf can cause this code to occur.
the spec at idle is 14kgh. 3502-3503 are eng misfire codes. poss loss or low fuel pressure can cause this also low fuel volume. Spec for the fuel filter is around 300kpa running (also the pressure should be steady and the needle on the gauge not bouncing) and it should not drop below 220kpa static within 20 min Volvo's recommendation of a 105k fuel filter change is way to long I prefer in the 15-30k range.

I have seen alot of MAFS go out from contamination, but in your case I would replace the fuel filter and recheck the pressures running and static to rule out the pump. Before you balk at the price of a filter replacement, part of the interior has to be dissasmbled, 3rd row seat, spare tire covers to access the filter and in the case of the fuel pump the driv line and ENTIRE rear suspension has to be dropped to access the pump and sender 8-12 hrs if you are in a rusty area.

Hope that Helps

Joe