fuel problem/

i have a j plate 940gl.every few days if the tank is less than 1/4 full and the reserve light is not lit the engine will cut out.it takes a few minutes to start,and when it does the emissions light comes on .when the codes are read they are always:- fuel (bosch)1-2-1(maf sensor signal absent or faulty). ignition 1-4-4 (load signal from fuel injection system absent or faulty).when the codes are cleared everything is ok for a few days.the local garage cleaned the contacts on the maf and i put some silicon sealent round the plug to keep moisture out, and changed the air filter ,oil and plugs last month, but the problem still occurs.i have been told by the garage to change the maf but thought to try here first.would running the tank that low cause the problem?can i do any thing myself to cure the two problems.also i think i read on a link that all volvo fuel gagues when they read 1/2 a tank of fuel there isnt 1/2 a tank ,as other cars would have is this correct?.