2003 Ford Taurus Engine dying at low RPM

Engine Performance problem
2003 Ford Taurus 6 cyl Front Wheel Drive Automatic

My 03 Taurus starts, runs with no problem except when slowing or stopping. At 40mph and slower when the rpm drops to idle, it will sometimes stall, more often than not. Most of the time, it will start right back. When it does fail to restart, turning it to off and then restarting resolves this issue. Sometimes it will die upon starting and will not idle, holding the accelerator down for a few seconds until it finds an idle works for this. If I try to let it coast along at above mentioned speeds, the rpm will bounce from a near stall to 1500 rpm like it's searching for idle speed.
The engine light never came on and nothing showed on code. I tried a new throttle postion sensor, new plugs, new fuel filter and new relay for the fuel pump.
I just got it back from a dealer that installed a new MAFS and battery. Thought it was fixed until about 20 miles and it started doing the same thing.