Background info
2002 f150 4x4. 5.4 engine, true duals and 6inch lift. No major engine work.

A few months back when i started the truck cold, it shuttered a little, turn it off, back on and nothing and it didn't do it again. About a month ago, my check engine light came on. Codes were P0171 and P0174, bank one and two too lean. So I started with checking vacuum lines , sprayed all the carb cleaner and no leaks. Replaced the pcv valve, no change. I have replaced the fuel filter and cleaned the maf. I couldn't change it and time got away and a few weeks later I tried starting it and it started idling really rough. Below 500rpms, I gave it gas and it helped a little, and after a minute it idled normally. Now it has gotten worse and even when I give it gas it will die, I will restart the truck and it will return to normal idle. I took it to multiple shops and no one can seem to figure out what the cause is.

Any thoughts as to a possible solution? Thanks in advance.

 

VACUUM LEAK...

Try starting it with the MAF Sensor electrical connector unplug.

 

Also, check the IAC valve.
Are you still getting the P0171/P0174?

 

yes I am still getting the codes and the IAC was checked and is functioning properly, I am not stalling at stoplights or when I'm just sitting which makes me rule out the IAC.

 

as stated before I went through every hose on the engine with carb cleaner, if something was leaking the carb cleaner would have caused a change in rpms, unless there is a hose I missed.

 

How many miles?
Did you check the entire intake manifold?

 

A faulty/leaking brake booster, missing/faulty o-ring on the dipstickt can also cause a vacuum leak. Leaking intake manifold gasket is the most common problem sending that codes. It's hard to detect vacuum leak using carb cleaner on V type engines. Just try disconnecting the Maf sensor to disable air metering mode. If it runs better without a MAF it's either a vacuum leak or faulty Maf sensor.

 

165,000 , and that is my next place to start, though carb cleaner didn't cause a change, it is possible it's leaking. Any ideas how to check it more throughly?

 

I am having the same problem with my 01 4.2l. I have gone through and changed all the gaskets on the intake manifold and still the same thing. New MAF new EGR new fuel filter new PCV new O2 sensors I have done a lot but it is still doing it and now it's even starting to sputter when it'r raining or foggy out. I have the bank 1 and 2 lean codes as well. Any ideas?

 

I'm having the same issue and it seems to only be when its cold.

I have replaced PCV elbows, cleaned throttle body, IAC, EGR. Replace plugs, Coils, Wires, Intake gasket. Granted it is running amazing 97% of the time for having 320K miles I would like to figure out why its shuttering more upon start up in the cold.