I have a 1998 5.4L Expedition, and it can run really rough at idle. After sitting for a while and if I start it up, it will run ok for a few minutes and then start to idle very rough. If I increase the rpm's, it "seems" not to be rough any more.

I get the following codes, P171, P174, P156, P151, P136, P132.

I cleaned the MAF sensor with MAF sensor cleaner, but that did not help. Based on research, it would seem that it is a vacuum leak because it runs rough at idle. Would this be a correct presumption?

I am a novice for knowing my way around the vacuum hoses/lines/etc. on this vehicle, so does anyone know how I navigate and find the vacuum leak? I could not seem to find any maps/diagrams/pictures such that I could start inspecting? Or is visual inspection futile in this case?

Thanks for any advice.

 

Check the PCV valve hose and the elbow all the way around back. Most common failure.

 

Here's a picture of the assembly. See the elbow as noted above as the first place to normally see the failure/vacuum leak.

https://www.flickr.com/photos/24918597@N08/7464456702

 

Did you examine the MAF real close to make sure the micro wire wasn't broken?

 

If the wire breaks, the PCM will set a new code.

Also check the inlet tube for loos attachments, grommets, etc.

 

- I visually inspected the PCV hose coming off the back by the firewall, but it is very difficult to get good eyes all the way around since it is really tucked back there by the firewall. I could really only see parts of it, but the hose in general appeared to be in good shape. I will have to see if I can get a camera back there and take some pictures. Or is there a way to spray something while running, like I saw in one video where brake cleaner was used? Or is this not an advisable technique.

- I will check the MAF sensor again to make sure the tiny wires were not broke per the previous post, but I thought it looked really nice. I will check again.

- Per a previous post as well, I will try to inspect hoses in daylight tomorrow. There are just so many hoses running all over the place that I do not know if they are all related to this vacuum / air intake.

 

Yes you can spray some carb cleaner or brake clean and see if the idle picks up. You really dont need to see it, you can do the ol reach around and feel it. Right at the bend were it goes from 1 inch to like 3/8ths, if it feels like mush and not hard rubber its bad. Dorman makes the replacement now, if you dont want to fuss with the dealer. Have fun, Good luck

 

The computer is usually too fast and you will never hear any difference in the idle. You need to monitor either the short term fuel trims or the upstream O2 sensor voltages to see the effect.

 

That actually works better if you bring the engine up slightly off idle first. At idle the IAC valve will regulate the RPMs, but once you're off idle the IAC is disabled.

 

Looks like it is the elbow way behind the back. When I felt with my finger behind without the engine running, it seemed like it was fine. But when I started it up and again put my finger around the elbow, I could feel the little leak. So just seems I need to get a new assembly.

- Is the F85Z-6C324-EA shown in one of the flickr.com links above the one I need for my 1998 Ford Expedition 5.4L Triton? The pic of this part looks very similiar to the part on my Expedition. I just am reading stuff about there being heated and non-heated versions. Just want to make sure I get order the right one since it seems these are not available at the auto stores.

- Do all the boots just pull off, and can I just yank without damaging something?

- I probably leave the current PCV in there, right? And not replace it?

 

In addition to my above questions, could I just replace the elbow with this elbow (Dorman 46017) from Advance Auto per link below? Or is the elbow meant to be "fused" to the hose, and that is why the entire assembly needs to be replaced?

Dorman - Help PCV End Assembly 46017: Find best PCV Elbow at Advance Auto Parts

 

You can just replace the elbow from Advanced Auto providing it's the only leak.
I'd start there as most only go bad at that point.

 

Sure can, and you'll save a lot of money in the process.

 

Well problem seems to be fixed. I replaced the elbow with the part from Advance Auto and I drove for 5 miles without any issue. I uploaded a photo below and now I know why I could not feel the crack with engine off....only could feel the air with engine off.

Thanks everyone for the input!

It was tough getting the part off and on, but here are the steps for what seemed to work for me....

1. You can see the elbow fully by looking from a little bit under the throttle body on passenger side. From this angle, I used an extra long flathead screwdriver to push the elbow off.

2. To hold the vacuum tube out to work on it a little easier, I tied a string with a slip knot around it to pull it out into the open more. This freed up both hands a little better.

3. Since the boot was really tight on to the vacuum tube, I used a utility knife to cut a slit in the boot being careful not to damage the vacuum tube.

4. With the string still tied to the tube, I put the the elbow on to the vacuum tube with a back and forth side-to-side motion. Took some effort and patience, but eventually got it all the way on.

5. I removed the string.

6. To get a better angle to now put the other part of the elbow on to the body, I jumped up on the engine bay right in the center with my knees over the radiator. This gave me the best angle with my left hand to use force with a side to side motion to get the elbow on. Again, took some good effort, but goes on nice and tight.





Elbow with crack.

 

Yeah, that's what they usually look like. That's why it was recommended days ago to check that specific part.