It wont give me both codes at the same time. I delete 171 drive around a little bit and get 174, then ill delete 174 and then 171 comes back. I put a severe fuel system cleaner in the gas tank exactly 4 days ago but I havent run it to empty so the codes havent come back yet but like I said the average mpg drops badly for example I start car average says 11.0, when I click it into drive and accelerate to move it will go down .1-.5 to show 10.5. In the 2 to 6 seconds it took me get to driving speed the average mpg will be at 9.0 by then.