Hey everyone
I'm new here to the forum but have been reading alot of the Threads. I have a 04 F150 5.4 liter with 140,000 miles that has been ideling rough for about 3 months now and no check engine light would ever come on then it started to buck and hesitate driving around 45 to 55mph when you ease into the gas when it is in park and you bring the idel up to 1 grand it drops down to 500 rpms and cycles over and over almost sounds like its going to stall. It has done this for 2 months and no mechanics could say what was wrong because there was no light. Well now there is a light and the code is p0171 (lean bank #1) i have checked for vacume leaks, cleaned the MAF sensor,fuel filter, air filter, had the injectors cleaned, and still nothing. Its at the Ford Dealership now and has been there for 4 days and they dont have a clue. they said that it has good fuel pressure they believean oil port is blocked and want to tear the motor down and check it. Is it possible that the cam phasers would make it run this way or a bad VCT maybe. This is crazy they want 600.00 dollars just to tear it down and another 600.00 to put it back together 1,200.00$ and they dont even know if they will find anything wrong. If any one can help please do.

 

Have you changed your plugs yet?

 

Maybe the MAF sensor is bad.

 

did you check the Coils? i have heard that rough idle has been associated with that quite a bit. not that it explains the code your getting....but it might be somewhere to start? did you try pulling the (-) battery cable for a couple of hours and then put it back on and see if the computer relearns after some of the stuff you have done to it?

 

Yes the Ford Dealership even tried to reprogram it and still the same thing. They are saying the engine is making alot of noise so they think that some thing has let go in it. Since I have has the truck it has always had a tick in the engine compartment

 

if you find out whats wrong, please let me know. that is exactly what mine is doing, except I am throwing a #5 misfire code as well

 

Mine was acting similar and it was a vacuum leak on the back side of the intake. It was throwing a lean code also. I had to take the intake off just to put the plug back on. May check into that.

 

no doubt, keep us informed because if i rev my 04 to about 1000 to 1200 it drops back down and back up again repetitively and wont stabilize until about 1500. when in drive, taking off, if i want to ease on the gas like, to just get it rolling, it will ease up to about 1000 rpm's then shoot to about 1800 without moving the pedal but i have no rough idle or codes though. lol, its kinda annoying when trying to hook to a trailer or ease through parking lots...

 

this sounds to me more like your transmission. so the motor runs fine but when you go to move its erratic? sounds like the tranny is slipping to me....but thats just my 2 cents

 

thought about that but, when it happens, if im on loose ground, i dig holes...lol its not the tranny because the truck lunges when it happens. theres no slip though. the wife has an 03 explorer with the 4.6 and the tranny went out and it was slipping, so i know that feeling, this is different though. just like as if you had pushed the pedal harder but you didnt. lol, my inlaws driveway is about 6-8 inches deep in new gravel and when i leave there it looks like i went, floored stop floored stop...haha. its more like a delay from the pedal to the engine, but only at an extreme easy take off.