After changing all 4 O2's ,pcv hose ,etc. ,as many did here, the problem was the MAF sensor.Local Ford dealer will inform other dealerships of the cure for these common & hard to pin down codes.I have a 5.4 '98 ,it seems to be a problem with that engine .Don't know about the 4.6,could be the cure for that one too?

They finally solved it by putting on & yanking off parts, something we all can't afford to do.Also interesting to note that most aftermarket air cleaners do not seal well so a Motorcraft is the best choice to avoid leaks in the air intake sys. , according to them.I don't know if Donalson makes one for the F-150 because I have one on my '98 Camaro & the rubber seal is enormous, compared to the GM one.That filter is a good choice, no chance of a bad seal, with it. IMO that is best filter on the market.

 

first off welcome!

second a dealer that has to "yank and replace" should be avoided! your MAF was prolly just dirty. there is a specific test proceedure for every single code these trucks produce and any dealer that doesn't follow them for a diagnosis of the problem should be avoided!

never ever let a dealer/mechanic fix/replace anyting without first outlining the test proceedure and steps followed to determine what work/parts are needed.

sensors and pcm codes are there to tell you that something is wrong not that the sensor needs replaced.

 

Thanx hcmq! I know that fix of the dealership seemed kind of unorthodox to say the least ,but this is a problem thats driving a lot of experienced Ford techs,& other exp. mech. (of course a lot of DIYers too) completely batty.There is a thread on it just today.The mysterious PO171&174 seems to baffle the best of them ,but believe it or not the MAF was cleaned to no avail.When it was replaced the codes ,after all the prescibed fixes,including a plug change & the infamous PCV elbow did not make the eng. malf. light go off permanatly,only the MAF change did it! Don't know why the PCM did not pick up the MAF as the culprit?

 

My '95 T-Bird did the samething twice, the last time week ago no codes no engine light. only mine would go to 4000rpm and it was like I was hitting the rev-limter the rev-limter comes in at 6000rpms its been chipped and other mods. I cleaned the mass air flow sensor, Tested it voltage was good I said that was it. 2 days later it did the samething. I just replaced no prblem so far.
Glade thay got it fixed. If it had been one of the dealers around this area,it would of probely took them a week or 2 to fix. I got mind at ford at first the parts guy said $316.00 I said look in the other price book,than he come back said it would cost me $210.00 12 month warnty if it broke bring it back and thay would give me a nother one.

SVTDSG03

 

I usually do not post much but due to the many variables of what could be causing this and the fact it is a pain in the a$$. Thanks to the forums! Yep! - P0171 & P0174 came on at the same time. Cleaned MAF - nope, replaced fuel filter - nope, changed PVC - nope. Started looking at the elbow and removed the whole thing and as I was looking at the elbow end which looked fine I decided to look at the PCV side, what ta you know there is a piece of hose about 2 in long that connects to the PCV and the tube assembly (opposite of elbow end). The hose had a large hole in it and you would think that I would have found it or felt it when I replaced the PCV. I reset the computer by removing neg for 5 mins and so far the codes have not reappeared. I do agree with everyone else when both codes come on. XLT150 4.6.