I also have a 97 Contour V6 - I just went through what I suspect might be your problem. When first realizing I had those two codes, I got cheap & pulled the battey cable off, to clear them. This worked for approx. a week, and then I got a third code P0420 - I ended up having a bad Cat. converter. The dealership fortunately covered it under the 80,000 mile emissions warranty. Immediately after the Cat was replaced, the same two codes came back P0174, P0171. The dealer informed me that I had an upper & lower intake leak. I ended up replacing both sets of intake gaskets myself, and the car is running fine. The procedures for doing this can be found in the How-To's. Hope this helps.
