starts hard...intermitent

I have a 98 explorer..4.0 6 cylinder.
My problem is the car normally starts fine but lately about once a week or
so it cranks over but won't start till I pump the crap out of the throttle.
Then it stalls and I go through the starting process 4-5 times and then it
seems to run fine. It will run ok for a week or so then it will happen
again.
Could it be the gas filter or fuel pump?...Any idea would be a great help.
Thanks
Tim