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

 

Generally if you have a vacuum leak it would cause the engine to have a higher than normal idle. take some carb cleaner and spray around the intake plenum if you find a change in idle quality you found the leak. The plastic intakes are common for leakage, Im not sureabout the 5.4 but other Ford engines intakes are 2 pieces and I have seen the seals go bad. If you are getting a lean code then either your sucking too much air or your O2's are jacked, since you replaced the O2's I would start spraying that carb cleaner

 

Thanks Phinxter, will give it a shot and let you know what happens this weekend. -Bamadoc

 

I have a 99 F 250 LD with 5.4 doing exactly the same thing with the same code and same idle problems. Spent $$$ at dealer diagnostics and they had no real answer. They had to phone Tech hotline and they are saying its a timing issue. I also have a K&N cold air intake which the dealer is saying could be the cause,but i dont know if i believe that because Ford sells a similar product from their performance catalogue. I also just had to replace the head gaskets and plane the heads,and again Ford is saying that planing the heads was wrong, and could be causing the timing problem....but the P0174 code was there BEFORE the gasket problem!! I know this isn't much help but they did clean the MAF sensor and code has not come back yet. This rough idle has been an issue sinse i bought the truck,and yes it is VERY FRUSTRATING that Ford says they cant explain or its NORMAL for some of these engines to idle rough HOGWASH!!!! It's only got 11500 kms on it and only 84000kms on it when i got it , and the idle was rough then. If you get any info or an actual answer please send me a note.

 

Hi 99250ld, I agree that this rough idle is not something to just be accepted. I did go back through the coils and found some corrosion up top at the spring but they were still ohming out right. Hopefully I will get it back together this weekend and have some good news. -Bamadoc

 

Bamadoc, Take a good long look at the MAF sensor,it's the only thing that was actually cleaned and took the p0174 code away on my truck.Hope you figure it out soon!

 

This is the code I know have on mine. Where is the MAF sensor?

 

should be in the air intake just behind the air filter.