i have a 1997 f150 with a 4.2 v6 in it just had the motor completely rebuilt in it. less than 3,000 miles ago but it is still doing the same thing as before i had it rebuilt it has three codes in the registry it says bank one lean and bank 2 lean( i am assuming this left side right side) and has a cylinder 5 miss fire. when it is cold after sitting all night and you start it it misses for about 10 min going down the road then sometimes it will stop other times i will not clear out for anything. if u come to a stop sign it will load up and start missing again/. just replaces plugs wires and coil pack along with both 02 sensors and egr valve the entire short block is a complete rebuild .020 over stock bore any ideas? i am wondering what is throwing the bank lean code if its not the o2 sensor also map and mass air sensor is new as well

 

also has two new fuel injectors

 

Check the IAC motor. They really give us fits in the cold weather times. If bad, you might be able to clean it up so or just replace it as they don't cost that much. Also check in throttle body and make sure it is clean and not all varnished up especially behind the butterfly. They cut off the air when they are cold if they are clogged. Clean the MAF. One more thing, check the PCV valve by the t/b. Most people don't. Good luck.

 

Did u replace the isolated bolts in the upper intake manifold? I'm assuming you installed new intake gaskets during the rebuild but the rubber grommets around the bolt are now to be a issue they suck air (vacuum leak) would explain the lean codes on both banks and rough running when first started but goes away as warmed up

 

Who did your engine rebuild and how much was it with parts and Labors