It could be a mix of a whole bunch of things try these:
Bad PVC
Vacuum Leak
Bad 02 Sensor
Dirty MAF
Dirty Air Filter
Intake Gaskets.

Try spraying WD-40 around the gaskets and se if the code goes away.

 

http://sites.google.com/site/fordf15...p0174fix/Home/
This website should help you, it shows the parts and detail repair. the isolator bolts that hold the plenum down leak vacuum causing your codes.
this will fix your concern

 

So I looked at that website and it was very good but that can't be my problem cuz I have a 5.4 and my intake looks nothing like that but for the original post from blazin that should easily walk you through it but if anyone still has any advice for ONLY PO174 not both lean codes for a 5.4 let me know.

 

Bad 02 sensor.

 

check your egr hose that goes to the back of your intake manifold,mine was split,and it wouldnt idle right,and i finally spotted it at the lake,and wrapped some duct tape around it till i got back to town and havent had a problem with it and that was close to 6000 miles ago

 

Had the same code. Below and at the back of the plenum there is a vacuum line with a 90 degree boot on it. (Looks like a sparkplug boot) They are bad about getting a hole in the elbow. Mine had a hole, but I had to remove the elbow and flex it to see it. Changed it out and code cleared and did'nt come back. I got the info from another website www.f150online.com I think, do a search and you should be able to find it.

 

yeah thats the EGR hose,that goes to the passenger side valve cover,i think the part was like $30.xx at my local dealership

 

Although that code wont affect how your truck runs, so unless you want the light gone just to see if another code pops up pull the light to your SES.