I just replaced the intake manifold (had a coolant leak at the crossover that was shorting the coils) on my 2001 f-150, 5.4. It runs great until it warms up and then it starts to miss. I get codes saying both banks are running lean and a missfire on the #1 cylinder. I'm thinking there could be a vacuum leak somewhere, maybe around the EGR since it is supposed to kick in when the engine is hot. Any thoughts are appreciated.

 

First, no the EGR does not 'kick' in when the motor warms up.
It does not work that way at all.
Second find the cause of cylinder 1 missfire, Asumming the code is a P0301.
Third, post the codes please, not what you think they mean.
Interpetation of codes is a big problem with many people.
Good luck.

 

Went to O'Reilies and got the codes:

PO171 System too lean (bank 1)

PO113 Intake Air Temp. Sensor 1, Circuit High Input

PO174 System too lean (bank 2)

PO301 Cylinder 1 misfire detected

As I said I just replaced the intake manifold and pretty much had everything connected to it taken off. I thought there might be a vacuum leak but I sure can't find one.

Thanks for any help.

 

Take a look a the IAT plugup. You likely did something to it putting it back togather.
The 171/174 code is likely an air leak.
You missed something.
At this point I would clear the codes and see what comes back.
If the motor is missing one cylinder repair that in any event.
If the CEL flashed, the cylinder in not fireing but the injector is still putting fuel in. Not good for the cats for that bank .
Coil/ injector plug etc.
Good luck.