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

[Berg]

did the part you bought have new elbows on both sides of it? the elbow on the end that connects by the throttle body on mine was melted closed.now its runs like a dream and even sounds different too

 

[glen615]

Yes the hose came with both elbows and the pcv.

Yesterday I replaced the MAS with a new one and that did nothing and I also replaced the fuel filter but no luck either. Tomorrow I will swap both upstream 02 sensors and possibly the fuel pressure regulator and after that I have no idea what else can be generatoring both P0171 & P0174 codes.

Also, yesterday I fed smoke through the brake booster line from a fog machine hoping to see it leak somewhere but it seemed airtight everywhere even checked under the car. I put s good amount of smoke in too

Taking a break today for the holiday but back at it again tomorrow. Have a happy thanksgiving!

 

[Berg]

sux !

 

[glen615]

Well it turns out it was the fuel pump. Just goes to show that the lean codes
generally associated with a vacuum leak can sometimes be a more involved. Fortunately I found a guy to drop the tank and replace it with all for under $450.

I returned the o2 sensors & fuel pressure regulator. I hope my experience helps someone.
Thanks for the input!!!

 

[Lane24]

Glad you found your problem !!! Like the title says , these vacuum leaks and simple things are what you need to check first before you let someone talk you into spending the $$$$$$... and a good percentage of the time that's all the problem is....but unfortunatley, sometimes the problem goes a little deeper. Thanks for sharing your experience in this thread. It's going to help someone for sure.

 

[ohillny]

Life and financial savers

I have exact same symptoms down to the whistling and being that it is -3 and -22 wind chill here in rochester the EX would not get me were I needed to be this morning thanks for this post I am sure this is my problem as I have the same codes and check engine light on since replacing my coils and plugs probably damaged that hose then.. Once again thanks for this post!!

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!!!

 

[ohillny]

she is stalling again

I replaced pcv and hose to the back of the intake was running a lil better clean MAF sensor still the same idle. Temp dropped last night this morning she was running real rough. I also was going to change the fuel vapor separator tube this is the one that goes to the brake booster. I don't think this is the problem but it kind of worn out also. Still I am at a lost any other suggestions? should I give the TB and that whole area a good cleaning? Suggestions are greatly welcomed..

 

[bedrck46]

You may want to clean the exhaust ports in the TB which involves removing the TB

also would suggest new plugs,cop's, etc

 

[ohillny]

THanks

Yeah gonna have to get in depth with it, seemed like I started having these problems after replacing all my plugs and coils honestly.. THanks again for the suggestions..

 

[bryanaceron]

Yeah gonna have to get in depth with it, seemed like I started having these problems after replacing all my plugs and coils honestly.. THanks again for the suggestions..

had the same problems did the same replacing all the parts and come to find out the new set of spark plugs were defected. now runs like a champ