96 f150 with the 300 inline six and 5 spd trans and dual tanks. i started off with the po171 and po174 lean codes. i was told to replace the o2 sensors so i did figuring it was, if nothing else, good maintenance. i cleared the codes and drove about 30 miles and the check light came back on. i replaced the plugs, wires, cap, rotor, and air filter as a tune-up. i also replaced the questionable vacuum lines and tested all of them by spraying carb cleaner around and found no change in idle. i cleared the codes and the light came back on. read the codes again and the po171 was gone but there were 2 new codes, a po401 and a po401 and the po174 was pending. the truck also sputters and stumbles for about 30 seconds at start up when it is hot but only when i use the front tank. i would really appreciate any advice i could get because i would hate to have to take it somewhere. thanks and sorry for the mini-novel

 

When you were spraying, did you check for an intake manifold leak?
The P0401 indicates a problem with the EGR system - the more likely causes are a faulty EGR differential pressure transmitter or a blocked tube.
The problem with the fuel tank being used could be that the screening filter inside the tank is clogged or the fuel pump is underperforming, leading to fuel starvation (lean condition).

 

Sounds like it could be a bad EGR valve. This would cause a lean condition and obviously the EGR codes.

 

i was thinking it was the egr but i didnt know if it would cause the lean codes or the problem with the hot starts. i had some problems with the egr on my 94 4.3L blazer and that was easy to fix but i have no idea where it is on the truck.