I had the same problems as listed above. It was a vacuum leak. Elbow up front and split tube in the back. Idles perfect now.

Thanks for the suggestions.

 

My Check engine light came on a few days ago and everything is running fine, i got the codes p0171 and p0174, i did testing on the MAF sensor and all checks out there, i checked the PVC system and found nothing wrong, besides the o2 sensors is there anything else it could be?

 

i have a 2004 F150 heritage XL edition with the 4.6l engine

 

It's not the O2 Sensors. They are doing their job and informing you there's a problem.

 

well i took it into ford and i guess my MAF sensors was bad...even though when i tested it it seem to be working fine.

 

That's strange, specially when both banks are positive for lean.

 

Troubleshooting those DTC's and MAF testing can be found @ Ford Scorpio. For anyone else having problems and haven't figured it out, - bottom of page here -

http://www.fordscorpio.co.uk/fuelmonitor.htm

 

well my light can back on and i was right my MAF was good to began with and its actually a fuel pressure problem....the pump is working fine, it losing pressure at the engine, so they have my truck for a few days while they test every point they can in the fuel line system, and once i know exactly where it was ill post with details. and the part that messed up the ford master tech was my truck is still running like a champ, and my question to him was how come he didnt test the fuel pressure the 1st time i took it in.

 

I was reading all your post and found my problem, 4.2 L engine, I sprayed two cans of brake cleaner trying to find the vacumm leak, I knew this was the problem but no luck, then you all came into my life, the tube that inserts into the right side valve cover (behind the coil packs) was not in the valve cover, I could hear a hissing noise up by the throttle body, well they put the PCV valve attached to the throttle body and run a plastic tube to the vavle cover, reinstalled and no check engine light,

 

my daughters truck 4.2L had the codes 171 and 174 I took the air cleaner apart and spray cleaned the MAF sensor after about 2 days the DTC went away. Hopefully it will stay away..

 

so wait i have this problem now and i cant seem to know wat it is i read some of this post but mine dosent do that i just shakes really bad when i drive it but when in park its smooth

 

Sorry I thought I had replied the fix for this I have had other sites I've posted. Ours turned out to be the dreaded intake manifold gasket was leaking . However it didn't cause the truck to run rough in our case.

I believe in your case I would somehow check fuel flow with would cause it to run rough. Good luck

 

Got these codes, read all 7 pages of this forum trying to get more insight into my particulars. its a 2000 f150 2wd 5.4 base model.
I have replaced the cats, o2s, plugs, COPs, cleaned injectors, cleaned MAFS, visually inspected the "elbow" and all vaccuum lines, intake gasket to the best of my abilities. Even did the starting fluid trick around the intake and cant come up with anything. Dont hear hissing, brakes are still firm, and seems to run fine. The CEL just came on yesterday first time for these 2 codes. I replaced the COPs last week im wondering if I bumped something? I have been getting about 265 miles per tank as of lately and it was about 325not long ago. I just went over everything again and I found one thing out of place, a small rigid line that was out from where it plugged into, I am including a picture with it circled in red also circled in blue the piece i believe is the ill fated "elbow" hoping someone can confirm I have identified it correctly. I am forced to drive this truck with these problems so the sooner I can catch whats wrong the better I will feel about this lol. Mileage is 202,xxx
http://i167.photobucket.com/albums/u...enginehose.jpg

 

 

Mine ended up being intake gasket leaking seems to be a common issue. Smoke test would confirm.