1997 Taurus bug: emissions, fuel, ?
 

I have a 97 Taurus with an elusive bug. I live about 45 minutes from work. When I drive there in the morning, I have no problems. On the way home, it will work okay for about a half hour, then it starts cutting out when I accelerate, almost like it is flooding with gas. When I attempt to accelerate, it seems to retard the engine. The symptoms grow worse with each application of the gas pedal, until I pull over and shut off the car. I then start it right back up and it runs perfectly for between one and five minutes, then repeats the pattern. Each time I shut it off and start it back up, the initial response to the gas pedal is correct, then it gets worse. When the car sits overnight, it is fine again the next morning. I have taken it to mechanics three times. Each comes up with some fuel system or emission system remedy, but they never drive it long enough to know it did not work. The fuel pump has been replaced twice. I have not been able to locate any pin-hole or anything in my vaccuum lines. Any advice?