97 expedition codes 171and 174

have a expedition engine is starting to hesitate and sputter when i stop at a stop .got these two codes off po 171 running lean bank 1 and po 174 running lean bank 2 looking threw the code book cand find what these codes mean.i had post up before regarding milky oil cap after loooking threw the motor found that the pcv valve was in the valve cover so i went and put a knew one in and that cleaned up the milky color know these codes poped up change the plugs and still doing same.runs fine when driving but when i come to a stop it almost dies out but it doesnt any ideas would be gratfull .....:banghead::banghead:cause im at a loss here ....

On the back of the intake manifold is a vacuum line connection. These are known to dry rot and split. It will throw the codes and also cause the vehicle to almost stall at a stop. I found this leak by applying a 5-10 psi pressure to the vacuum system and listened for the air leak. The vacuum lines run to the PVC valve and a couple other places. I bought the replacement vacuum lines from Ford. It's a bit of a combo manifold of vacuum lines.