I don't know if this is it or not, but years ago my wife's car did this. It ran fine the day before. It turn out to be the catalytic converter was clogged up. Try putting your hand near the exhaust pipe and see how much exhaust is coming out. Good luck. Are you getting P0171 and P0174 'check engine' error / trouble scan codes? (indicate a lean condition Bank 1 and Bank 2, respectively)
See "Related Questions" below for another possible cause, that involves leaking intake ports.