how do i fixs this problem?

i just got this  1997 jeep Cherokee.  When i crank it up it will do just fine but
when i put it in gear and touch the gas pedal to go and git in it at all it will die
but if i drop it down it will stay running.but in park and i give it gas it will stay
running.this is only ride any ideas? i don't no motor size but is 4 wheel drive.