1997 Ford Taurus DOHC with codes P0171 and P0174 running really rich.

how many miles on the car? i have seen O2 sensors get really dirty where they cant read the exhaust which results in the computer thinking the car is running lean and keeps addin or richining the fuel mixture. end result is bad milage car running rich fowled sparkplugs and O2 sensors. another option wuld be the air intake temp sensor. if it is reading cold it will make the computer think the car just started and run with the "choke" on.

CK FOR VACCUM LEAKS WITH SMOKE MACH IF THATS OK IT COULD BE SEVERAL ISSUES LIKE FUEL INJ MASS AIR FLOW OR FUEL PRESSURE. MOST LIKELY MED VAC LEAK

have scanned for codes .If none...vacuumleaks , fuel pressure then maybe temp sensor (but if that's stuck@-40degrees then it should be setting a code.Clogged exhaust?

p0171 indicates that it is actually running lean (bank 1) p0174 is system running too lean as-well (bank 2) this means that both oxygen sensors before and after the cat are reading high levels of oxygen and low levels of fuel. Have you checked for any vacuum leaks? Fuel pressure, fuel filter, leaking fuel line, or exhaust leaks? codes p0172/p0175 are codes for running rich