I have a 1997 Ford Taurus LX 3.0 DOHC. The car runs beautifully, but failed smog with high HC. I've replaced Spark plugs, wires, coil, egr valve, all 02 sensors, maf sensor, coolant temperature sensor, air temperature sensor, pcv valve, numerous hoses, vacuum lines, vacuum fittings/connectors, air filter. I have not yet retaken the smog test, but right after I replaced the maf sensor, coolant temperature sensor, and air temperature sensor, I now have the check engine light on after those three things replaced. The code is P0174 which means lean fuel mixture, from what I have gathered on the internet, but what else can be causing this? I'm perplexed.