IF there is no PVC valve on 98 ford tarus 24 valve dohc v6 engine what do you think causes codes PO171 PO174?

everyone says po171 and npo174 are map sensor problems, i do not think so, the egr pressure sensor collects vaccum and tells computer about the egr , what i am finding ,especially in winter, the 2 hoses going to the pressure sensor get full of crud and the sensor cant read anymore.Today i found a 1997 ranger with po171 and po174 codes ,the hoses were fine but ice had built up inside the knozles of the egr valve pressure sensor causing it not to read.check hoses and look for vaccum leaks first. I concur with the vacuum leak. To find, spray carb cleaner around all suspect hoses and manifold areas with engine at idle. When the idle speed increases, you have found the vacuum leak!