1998 Taurus SE Duratec 3.0 V6 Idles irradically

1998 Taurus SE Duratec 3.0 v6 ohc auto overdrive Idles irradically runs high at start then drops off until it then stalls also check engine light on. Did code scan, changed that sensor and also did tuneup (plugs, wires, pcv valve, air filter, oil filter and oil change also new plenum gasket then reset codes. Still running the same after all that. Ran it long enough for the check engine light to come back on. Did code scan again, this time came up as a different sensor. I have yet to replace this next sensor. I guess this would be my question, is it possible something else would cause this cycling of misdiagnoses about the sensors, if so, what? Or will I have to replace it all? Or have you seen this before on others and it all lead to a simple solution? (And now I have yet another problem with the vehicle discharging my battery while just sitting there, took the battery from another vehicle (fully charged)and put it in and it discharged that one also. Only thing I see that may discharge it is the flashing theft light which I have no idea how to disarm(all lights off, key in the off position ) or maybe an internal alternator problem not sure of that until I have it tested.) I unfortunately am limited by the amount of cash I can just throw away at this point, I also take care of my girlfriend which makes this even worse because this is the vehicle I use to take her to her appointments. Well used to. I now have to look to borrowing a vehicle that I can load her into, she really does not like my truck. The little bit of cash I get each month is gone before I even get it for rent and utilities, If you do not wish to answer I will understand. Thank You For Your Time and Knowledge!