Why does motor rev-up,by itself,then idle then sputter and die out

Question

1988 Ford F150,302 v-8,gas.When running good, all at once it dies out while idling,thats when the trouble starts.Motor revs-up for afew seconds,then acts like ur playing with the gas pedal for afew seconds.Someone said tap on the air bypass valve.It did run good each i tapped it.Replaced it,didn't help.Put new gasket on throttle body,didn't help.I read about the TPS,would that cause my promblems.