Ford Repair: 2000 Ford Focus LX dies out, ford focus lx, brand new car

Question
Recently my Focus went from driving like a brand new car to idling very rough(sounds like helicopter)..we changed wires and plugs and it ran great again for about 6months..then it started again..replaced wires,plugs,air filter, PCV valve(twice)and checked for exhaust problems to no avail..Engine light comes on and we have had several mechanics try to read it for us and they keep telling us that they are not able to read it...This car does not run well at all now..you have to keep a foot on gas at all times or it will cut off on you and even then it stalls out alot..could the positive battery cable being bad cause this to happen as it is badly corroded ever time we clean it. Need help desperately as this is my only car.  Smells like it is flooded all the time too.

Answer
will those cars have alot of problems with fuel pump which i think they extended the warranty on that part of car for 10 years 100,000 miles dont undersatnd y they cant get any codes i would drive to a auto zone  and they will get the codes out for u for free and write back with teh code and i will give u more info , but sounds like fuel pump