I have a 1986 240. Bought it about 2 years ago from a shop that specializes in Volvos. Ever since I have had it the gas mileage has been poor, approx 13/14 miles a gallon. About 3 months after having the car, I let another Volvo repair shop talk me into replacing the air mass meter ($600) that they said would dramatically help increase the gas mileage and fix the no power going up hills problem I was having. It solved the no power going up hills problem but did nothing to fix the poor mileage. Just after the new year it stalled once while driving, I restarted it & got home. Next day I tried to start it (from cold) it turned over but would not start. Now it has been sitting in the garage for 3 weeks. (It's my daughter's car she's at College). I finally got a mobile mechanic to look at it to see what was wrong. He said it has compression, a spark, no exhaust blockage and fuel pressure however he says that no fuel seems to be coming out of the injectors. He consulted a volvo repair shop and they reccommended replacing 'the computer' with a used one ($125).

My questions are:

1) Is it really 'the computer' that's crapped out or is it something else causing the car not to start?
2) Why the bad gas mileage and any suggestions to make it better?
2) Would replacing the O2 sensor help the poor mileage situation?

Thanks