Loss of power

I just bought this car online. He said it has been sitting up for about three months. He also said it was a bad fuel pump or filter. I changed the oil. When I step on the gas it will accelerate momentarily but loses its power very fast. You can hold the gas pedal down and all it does is rev up with no movement. I can turn the ignition off for a few minutes and crank it back up and it will go for a minute again and stop. It has fuel going to the pump because I did a test. Please help.