Hyundai Repair: my 2000 elantra wont start and drains my battery, hyundai elantra, 2000 hyundai elantra

Question
I have a 2000 hyundai elantra that was sitting for 3 months before i  brought it. My mechanics at my job said that it needed a fuel pump they changed it before i brought it. My computer was reading 4 misfiring cylinders but i only have a 4 cylinder car. Now they are telling me that my computer is bad and not reading at all. When the car used to drive for a while it used to hesitate and decelerate. when i pressed the gas and it decelerates the pedal feels like it has air inside

Answer
I'm not sure what you mean when you say the pedal feels like it has air in it.  However, four misfiring cylinders combined with a lack of power, worse the farther the pedal is depressed, worse as the car is driven longer, is entirely consistent with a faulty fuel pump.  I question the idea that the computer is defective.  This is a very rare problem.  By the same token, I'm not in a position to inspect the vehicle, whereas the shop is.

One possiblity is that the fuel tank or filler neck has rusted due to the vehicle sitting.  If this rust gets in the fuel pump, it will quickly ruin even a new fuel pump.