Hey guys, I am hoping someone might have some suggestions for my 99 f150 5.4L.
Here is the story leading up to now....I have inherited this truck from someone in the family who kept it on the minimum maintenance plan (dont fix until its dead). So to say the least this thing had all kinds of probs by the time I got it. But, the engine was always strong and had a great idle. Pretty much ran like new. Just looked rough.
About 3 months ago my wife gets hit in the bed of the truck by some guy who decided to run a red. Sending both of them across a 4 lane highway. Only damage to our truck was in the bed and frame shackles. Insurance made the truck look great again (was bad to begin with) with a new bed and pain job. When I get the truck back it has a hard idle as soon as it warms up and gives the code for lean bank #2. I have spent tons of time monkeying around with this thing trying to figure out what is causing this code and harsh idle. When cold it runs what feels like pretty good. As soon as it warms up it feels like a misfire or something. The idle is better when in park but gets worse when in gear.

Now to what Ive done. First took it to the dealer and he said check the IAC. ->replaced it. =no change.
ok, so check the plugs and coils. Not bad. They all looked clean and slight white haze. I did find the rotten pcv vaccum line and replaced the whole thing. Also changed or checked parts are DPFE, MAF sensor, fuel rail and pressure, EGR valve, throttle body, new fuel injectors, new O2 sensors (precat) ,all hoses and vaccum lines. I have even pulled the intake to see if there was a leak there or under the manifold (plenium?). Didnt find any. Did replace all plugs while engine was apart. Much easier when apart. I have been using a actron code scanner to check and clear the codes. But when I reassemble the truck I get the same bad idle when warm and same code p0174. My brother in law did put a k+N filter on there. I wish I had the stock unit to put back on. I did try cleaning it and the MAF which was dirty. Still no change. I tried taking a hose and listen for vaccum leaks around the engine and thought I might have heard something down under the intake. So now to the point of being ridiculous I pulled her apart again to see if I missed anything under the intake. Does that plastic box under the intake ever leak around the seams? I saw that it is made up of 2 halves and is glued together. Not sure how to test it. I dont see any cracks in it or the intake. I would have given up by now but this thing is a quest now. Its me or this engine! Do you guys have any ideas?

A side note: when I checked the fuel pressure yesterday it was 29.5-30 and book says it should read 30. That is fine isnt it? When I unplugged the vaccum line from the pressure reg it jumped up to 45 which is normal from my understanding too. I did read something about a propane vaccum leak test but have no idea whaty that is or how to do it.

I sure would appreciate any insight you guys have at this point and it might just keep me from pulling out what few hairs I have left. -Bamadoc

 

The fuel pressure is fine. Maybe you have a partially clogged injector causing the lean condition. I worked on a Ranger that had a bad injector. It clicked but didn't spray. He drove it long enough to burn a valve from the lean condition.

 

K&N filters eat up MAF due to the oil on the filters contaminating the MAF.

 

Only if over oiled!!!