Why does my 96 nissan maxima rev up and down when i hold the throttle?

it idled rough so i changed the tps after i changed it i cranked it up and it idles fine so i went to take it around the block and when i accelerated i would rev up and down like i was pressing and releasing the gas pedal so i changed the tps back and its the same problem so then i did the maf sensor that did not solve the problem then i was told it could be the idle air control valve but i'm no mechanic and don't have the money to buy it if it's not the problem