I had a 2004 Taurus with similar symptoms. In my case, however, there was an engine check light on. When hooked up to the diagnostic computer it gave a message saying “camshaft sensor error”. The Ford dealership was unable to diagnose the problem.
Putting too much unburned fuel through the exhaust caused the catalytic converters to plug (there are 3 on a Taurus) and Ford kept replacing catalytic converters ($600) until the warranty ran out. When the warranty ran out, I got rid of the vehicle.
Looking back, I think the camshaft error message was actually indicating a problem with the timing of fuel injection and a good mechanic could probably have figured it out. Unfortunately, dealerships don’t have good mechanics, just parts replacers.
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