I was reading forums on the 171 and 174 codes because my truck flashed the check engine light with those coming up. A lot of the symptoms I was reading was what I was experincing. I found out the hard way that a lot of ford engines will not operate correctly using ethanol gas! I bought a tank of gas of that stuff because it was cheaper. And that is exactly what I got! It ran fine on the way home. Ran fine after warm-up, mostly. I started it up the next morning and it was a mite rough starting. Check engine came on and it read all kinds of stuff like miss-firing cylinders, PO-420 catalyst threshold and oxy-sensor codes! Well I ran the tank dry and filled up with the real stuff "87 octane", cleared the codes and all and haven't a problem since 6000 miles ago! Just figured that I would let y'all know if you have or had these problems with using gas with ethanol!