SES light keeps coming on (forgot to write down the code), and says that bank 1 is running too lean. It only comes on after idling for a bit. Its a 02 F150 with a 4.6l, any ideas on where to start? Already has new plugs and cops.

 

This is a common problme on the f150s.
Do a search on P0171 and 0174 (right and left banks lean)
Reach behind the throttle body and check the elbow there. It melts all the time throwing the code. The elbow is connected to the PCV valve via a plastic hose.
Good luck

 

if the elbow is ok its your MAF starting to go...

 

Well, I just got Dual exhaust done on my truck a month ago, and have been slowly getting a leak from where the manifold meets the pipe. After doing the research on here I found a member with the same issue and it turns out that its the same code and it indicates and exhaust leak. Gonna go back to my exhaust guy and have him straighten it out and see if the SES light stays off.

 

I dont know about that.
I recently went through a ton of ***** with mine on those codes (0171 and 0174) and I still have them. Its really pissing me off cause the vehicle runs great!
Here is what I have and what i've done:
Hypertech III 87 tuning
K&N drop in filter
JBA 3.5" single side out exhaust

To date I have done the following:
4 new O2 sensors
New MAF
replaced elbow at back of TB cause it melted through
checked all lines and hoses
cleaned TB ports
flashed computer
intake manifold gasket is good
pcv seems to be working fine (has suction)
replaced egr valve
egr regulator
dpfe sensor

so WTF is going on?

 

if the light comes on after a short idle period - One of your O2's must be producing it .

Your O2's are Dormant @ start - Truck warms up a little - they become active and start switching .

Sounds like that's when your getting your Check engine light..