This is my first post, so please bear with me. I have a 98 exp 5.4 with 70,000 and no mods. Since the 30 day warranty ran out about 2 months ago, is has had a horrible idle. By this, I mean that it: occurs only at normal operating temprerature, no CEL, goes away once I excelerate, and is not present in park/neutral. Performance does not appear impacted, but VERY annoying with the shaking. It gets much worse with the AC on. Ambient temp is of no consequence. Attempts to fix include: clean TB, replace IAC, check vacuum leaks, sifted through hundreds of posts re rough idle on this site and others. I have been told it is normal by the dealership. Any suggestions much appreciated.

 

check/ replace dpfe sensor clean egr valve and tube. search engine section for rough idle.

 

What about a coil pack?

 

Also, if i remember correctly, about four or five years ago, there was a discussion about fixing the rough idle by moving and tying back a wire bundle away from the A/C accumulator, or something like that. As D said, a search is your best bet.

 

Hey, thanks for the replys. I just completed a search that consisted of about 50 different posts and close to 1000 pages of replys. I started a new thead because my situation appeared uniqe as compared to the other rough idle posts.

I found several posts related to the wiring harness, but I am not sure where it would be. There was a link to picture of where this thing is, but it would not come up (unavailable or something like that). Can anyone direct me as to where to look.

I will try and check/replace the dpfe sensor and clean the egr valve and tube. I'm not sure what or where the dpfe sensor is and I THINK the egr valve is in the throttle body itself?. I will search both, but if someone is willing to save me some time...

As far as the coil pack suggestion, would it only occur at idle and normal operating temp? I'm afraid I'm not knowledgable in this area, but my thoughts are that it would occur all the time or at least under load. Any thoughts?

Anyway, thanks to everyone!

Oh, yea, I've also replaced the fuel filter.

 

Something you might want to try that is very cheap is replacing the PCV valve. Only around $5 and for some it has cured the rough idle problem with the 5.4 L

 

Thanks! In fact, I was planning to replace the PCV valve the same time as the IAC. However, Pep Boys was out of them. I'm wanting to pretty much has this diagnosed before throwing too much money at her. PCV's are cheap.

I searched DPFE and egr valves. I may be a little confused after looking at the numerous pages of info, but it seems those things throw codes and cause problems sounding a little diff from mine. I will try to clean the ports, though.

 

I don't have any Pep Boys where I live so I don't know which brands they carry, but I would go with a Motorcraft PCV Valve. You may spend $2-3 more on it, but from the posts in the engines forum it is worth it. I just bought a PCV valve from AutoZone to fix a buzzing problem I was having with the orginal one. The new one is metal so it sounds the same as the worn out OEM one, but the idle on my truck is smoother. Within the next couple of months I will be making a trip to the dealership for a Motorcraft PCV valve. Figured I would get my $3.20 worth from the cheap metal one I bought and then put a true tested part back on there.

 

I have a '98 4x4 with the 5.4. I had the same problem a while back. It was just like I had put some WAY CHEAP gas in my truck.

I undertook the painstaking task of new plugs. Although the truck needed them, it didn't help my problem.

I started searching the forum for a solution. I found two good ones. I tried two things at the same time. I wish now that I had done them one at a time to see exactly which one worked.

I read on one of the engine forums about pulling the main harness away from the a/c evaporator. I know it sounds funny but check out this link to the thread. https://www.f150online.com/forums/sh...ht=main+harness

Second, I cleaned the MAF Mass Airflow Sensor. It was NASTY! Here is a link to one of the sponsors with a detailed description on how to do it. http://www.fordf150.net/howto/clean...flow-sensor.php

Like I said, I did both of these and no more pinging or rough idle!

 

Thanks for the reply. I pulled the MAF sensor a while back, but I didn't clean it as it looked brand new. I may clean anyway, just to see what happens. I also found info regarding the wiring harness, however, the link was no longer available. Your link gives the same message (file lost or missing). Anyway, I don't know where the evap is to even look for the harness. Can you give me an idea of what to look for and where? Thanks again for your help.

Chris

 

ckabee1, I don't know if the DPFE sensor will correct your problem. If you have never changed your DPFE sensor though, it wouldn't hurt. My 96 F-150 with a 351w had the first one replaced after only 3 years and I just got 6 years out of my last one. The newer ones are plastic now. My old one was metal and held together by rivets. Out of curiosity I drilled out the rivets and opened up the DPFE sensor to see what the inside looked like. I might have put 60,000 miles on this sensor and it was foul looking. The local Ford Parts
Dept says that this a high failure rate sensor. I installed my newest one and it took away the slight rough idle that had recently developed which I thought was probably due to a needed tune-up. I know that no one likes to throw money at parts that are not needed but this would be one part that I would consider a mileage change item. I plan to take pictures of the DPFE sensor opened up and post them when I get a chance. Just my 2 cents. Good Luck

 

The air conditioner evaporator is the black tube on the passenger's side firewall. In the summer time, it will have alot of condensation or frost on it after running the a/c.

 

Thanks for the replys. TracyLPatt, what were the symptoms of the faulty DPFE? My Expy idles poorly in gear and normal operating temp only, and gets worse with the AC on. It goes away when I accelerate. I have not CEL and has not stalled. It sort of shakes the truck, rather than feel like the traditional spark miss related idle. Did your DPFE throw a code?

bwmcintosh, my wife is out of town , but in the truck , so it will be this weekend when I can check out the ac evaporator. How difficult is it to find this thing? I remember that side of the engine bay being rather busy; is it near the top or bottom of the fire wall? About how big around is this thing?

Thanks many times!

 

What is a DPFE sensor? Where?