1995 Ford Taurus idling in park

When I first start the car it runs fine until after 3-5 minutes or if I give it some gas then it starts to rev up then down until eventually stalling and engine dies, I changed fuel filters, plugs, cleaned air intake and filter, changed oil, dropped gas tank and empied old gas rinsed with clean gas and refilled tank, on and on but cant cure this problem any ideas?Thanks for your time, from Stephen Armand.