Rough idle? P0171, P0174? Here's what you need to check first!!!

[ardjaye4]

Very common symptoms we all have at one time or another with our 5.4L is a rough idle where we will have high idle for a few seconds when slowing or coming to a stop followed by a drop off to a very low rough idle after stopped for a few seconds sometimes even to the point of stalling out.

I had this problem for a few weeks, and then the weather turned cold, and it got even worse to the point that my ‘ check engine light’ was even coming on. I took it to the dealer, and they replaced my IAC. No change. Still idled rough. Still had the CEL. The only change was the weight of my wallet!! So I turned to the internet!!!

By doing some ( a lot) of research on the subject from other Ford sites and forums, this is a culmination of what I’ve found out. The fix is a little rubber ’boot’ or elbow with a crack or a hole in it causing a vacuum leak.

The Ford dealer will run a diagnostic and indicate that it returned an error code P0171 and P0174, which indicates the engine is running lean. They will most likely recommended the following service:
Replace EGR valve - Replace PCV valve - Replace differential feedback EGR sensor -Replace mass airflow sensor -clean fuel injectors
all at a cost of almost $800. Yikes!!!!

The first thing to check is your vacuum assembly. You most likely have crack or hole in the little rubber elbow that connects to the intake from the PCV valve on the right hand side of engine. Even the slightest crack will allow more air to be sucked into the engine causing a too lean mixture.

The PCV valve is in the right valve cover... which is on the left side when your facing the engine (passenger side). It's under a lot of other hoses so it is very hard to see.. The hose goes back from the valve, then toward the drivers side to attach to the back of the intake way back between the engine and the firewall very close to the top of the engine. The common faulty part is the rubber boot that connects the hose to the back of the intake.

The way I found it was to follow the hose back from the valve cover. I sat right on the engine shroud, and felt for the tube sticking out of the top rear of the valve cover on the passenger side of the engine. With the engine off, it pretty much just pulled out and went back in real easy. Then I just followed it with my hand the best I could ( with the motor now running so be careful!!) until I got back to the firewall, and it actually comes up from underneath the rear of the intake. . You can kinda reach your finger up under there to where it's connected, and feel and hear a definate shoosh sound when your finger goes over the hole or crack in the elbow.. You can't see it, but you can definatley trace it back by following that tube. You'll know it when you find it because your finger will plug the hole, and your truck will start running smooth again!!!

The part number for the entire vacuum assembly with the correct boot on it is - F85Z-6C324-AA probably around $30 -$40. Or you might be able to just replace the elbow itself. Either way, make sure if you do have the leak, to make sure you have the replacement part handy before you take off the old one, because it will crumble in your fingers!!

Hopefully you just saved a few $100, and a lot of frustration. I know I was pretty happy when I found this easy fix!! Good luck!!!

hey good info. i have same code om my 2000 expedition PO174. how do i fix the vacuum leak & will that part# fit my truck also?
thnks

 

[Lane24]

hey good info. i have same code om my 2000 expedition PO174. how do i fix the vacuum leak & will that part# fit my truck also?
thnks

You replace the hose that this entire thread is written about. There are updates to the part # throughout. Take one of the #'s of the PCV hose to the dealer, and they will be able to get you the exact one you need for your year. ( and it won't hurt to clean your MAF.. there is instructions on that as well )

 

[Lane24]

It's the Mass Air Flow sensor. It's located in the air inlet tube that comes from where your air cleaner/filter is. Just disconnect your air inlet tube ahead of the sensor, and spray some MAF cleaner through the screen at the little elements in the center of the sensor. Let it sit for 5 minutes or so...,give it another shot, let it sit for another 5 minutes, then start your engine. Some people just use electronics cleaner, but I recommend actual MAF cleaner from the auto parts store. You can also take the sensor right out and clean it that way too, but it's easiest to just spray it where it is. You can hold a rag or something behind it. Here's a pic of what you are looking for. Mine looks a little different on my engine, but it's pretty much the same idea.

Just in case you can't find it....

 

[Kevo]

ok so ive read all of these posts related to the po 171 174 codes and my issue doesnt quite fit what ive read ok first of all about a month ago i did an oil flush, oil change, seafoam, and cleaned my maf, then about 100 miles later i get the code for bank 1 lean but it litterally ran no different but i took a trip from tacoma-spokane approx 500 miles round trip and it was getting only 13 mpg hwy when i normally get 17 mixed driving then the next day getting on the freeway it started missing like crazy and ran like crap all the way home and the CEL went from being on solid to flashing so i pulled the codes and got the 174 and one for cylendar 4 missfire, im sure the coil pack is going out. it runs fine when its cold but once i drive 3-4 miles it starts missing bad then the longer i let it sit the longer it runs good for before the missfire starts the next day. ive felt around the pcv hose and the valve and it doesnt seem to have any leaks the only thing ive ever noticed is a very slight whistle when i first take off from a stop... i want to think the coil pack caused it or i may actually need an O2 sensor but im seriously debating just replacing the PCV line since its only $40.

 

[FordandPolaris]

Probably heard enough thank you's for this write-up, but this was exactly what has been plaguing my truck for almost a year. I found my PCV valve was actually unplugged from the valve cover, and when i plugged it in, the idle went way downhill. I went and bought the replacement valve and elbow, and install was fairly easy. Now she idles like new, thanks again for the write-up.

 

[racerx4202006]

Thanks!!!

Thanks so much. Found it broken. 6.99 part at Autozone!!! Give them the FORD part number and they'll find it!!!
Saved SO MUCH!!!!

 

[bulldog77]

These codes just popped up on my 97 but it still idles fine. The k&n looks a little dirty but not bad. Truck seems to still run fine just the annoying light was on. Is it still the boot our is it something else?

Sent from my DROID RAZR using Tapatalk 2

 

[BillySquier]

Not sure if this will help many but I suffered from the same issues with low idle for some time and found an issue I'm sure many of you may have. There is a vacum line that runs into the intake manifold on the drivers side of the engine. The opening that this line feeds can become clogged and effect the idle. To fix this you must remove the upper part of the intake manifold and and locate the clogged passage way and then clean it out of carbon. When I did mine about two years ago it was so packed with carbon or whatever it is that I had to use a small chisel or screw driver and chip it away with soft hits of a rubber malett. Once I cleared all the crud from the upper intake it ran like new for a couple years until it developed the same issue, which I fixed with the same process. I'm not sure if this is the same for the 5.4L but it certainly made a world of difference in my 4.6L. Couple items had to be removed to gain access but in total this should take a person 2 hours or so with basic hand tools.

 

[joneskt]

Jet MAF

has any replaced their MAF with and upgraded aftermarket? the only one i find online is for $500...uhm...yeah...not getting that one...

I installed the Jet MAF a couple years ago, along with a cold air intake, Edge programmer, flowmaster exhaust, billet torque converter, aftermarket tranny cooler, and a heavy duty tranny rebuild. I have a 2000 5.4L, XLT, 4x4 and can get 17mpg highway. It takes a couple or few days though for your computer to relearn the new MAF sensor, meaning it was idling erratically. But after it's done learning, it was great!

 

[buildingdoc]

Okay. Just installed new hose assy. Still have codes 171 and 174. Cleaned the MAC yesterday and Iat checked out fine by ohm to temp chart. Thinking the market is bad. Also I went through half a tank in about 120 miles. 04 expy 4.6.