Ok, my 2002 F150 4.6 threw these two codes late last week. Took it to Autozone where they read the codes. First, i cleaned the MAF, reset the light. It came back on. Next, replaced the MAF, reset the light, came back on. Now, it idles rough after it's warmed up and shut off a few times at traffic lights. I am thinking it's a vacuum leak. Anyone here have any experiance with this?

 

On the 171 possible causes:

fuel pressure regulator malfunctioning
fuel filter plugged
fuel pump weak
evap canister purge valve leaking
fuel pressure sensor incorrect reading.

air leaks after the MAF
Vacuum leaks
PCV valve stuck open

exhaust leaks before the oxygen sensors

EGR valve tube/gasket leak
EVR solenoid vacuum leak

174 gives the same possible causes.
Check for a vacuum leak is my suggestion.
Where did u get the air mass meter from?
Secondary air injection damaged or malfunctioning or mechanically stuck valve.

 

Bought the MAF from Advanced auto parts... didn't make a change in the truck performance.

 

Good they will take it back if u find a vacuum leak.

 

check your intake plenum for a leak. it may be hard to find but if you use a can of carb cleaner and spary it down it will idle up if there is a leak. sometimes you need to use a scan tool with an o2 sensor graph to find it. but the plenum tends to be a common place for leaks.