I have the p0171 & p0174 codes. I have the 4.6 with 190,000 miles. I cleaned the MAF, TB, IAC. replaced OCCur valve and used 3/8" fuel hose to replace stock hose. also replaced a hose from MBC to motor (IAC?). I have another hose on order from dealer to replace line from valve cover on driver side to air intake right before the TB (idk what that hose is for)replaced fuel filter and pressure is good. air filter is a Fram. voltages on injectors was good. ran SeaFoam thru intake with almost no smoke.
so now I need to head in a new direction which is checking intake gaskets for a leak. I have heard of a smoke test and a propane test but do not know if these are good tests or how to do them. any help or advice would be greatly appreciated.