2014 Ford Taurus 3.5 liter

Most " mechanics " like something they can replace and be done . Oddball problems like yours is not their favorite . I assume someone else replaced the plugs , most every used vehicle I've bought had plugs not tightened properly . Go to auto zoo and have them read the codes , the clerk is not a technician they sell parts .

2014, could be a transmission solenoid problem like the torque converter lockup solenoid sticking so it kills then engine when coming to a stop, then the transmission pressures drop out and the solenoid releases, so it starts right back up until it does it again. other things are dirty throttle body, dirty or inoperative ISC unit, PSPS not working so the engine is not idled up during slow speed maneuvers, so the engine stalls out. You might want to consider a live data scan however you need to find a shop that knows what they are doing.