1998 Expedition - Misses at low RPM's

[JohnB]

Hello all,

Looking for some potential guidance..

I have a 98 Ford Expedition, 5.4L. It runs very rough at RPM's below 1500RPM. I can drop into 2nd gear and it runs fine at 2000RPM or higher,... then back to "D", and runs rough. Been doing this for a few months now.. Haven't been driving it much.

Research is pointing me towards replacing the Coils/plugs... however, coils/plugs were replaced 2 summers ago. (not by me, my father-in-law had the work done at a local shop, so I cannot confirm it was actually done)

My gut tells me that I should put in new coils and plugs.. but, I'm a little hesitant to spend the money on something that "supposedly" has already been done recently.

Could it be something else?

- I just replaced fuel filter 2 months ago.
- Had somebody tell me it was an exhaust manifold leak.. Not sure it is, as it only occurs at low RPM's.

Thank you in advance. I appreciate it.

 

[Jeff55v]

My ‘98 ran like crap when I bought it last summer. The first thing I found was a damaged air duct going to the throttle body. It looked as if someone carelessly jammed the duct onto the throttle body and didn’t get it over the lip on the bottom. This allowed air into the engine that wasn’t being metered by the MAF sensor. I replaced the damaged duct, and it helped the engine a lot.
I also had to replace all my plugs and coils. If you decide to replace those, use the best parts you can, so hopefully you’ll never have to do it again. (It really sucks) While you’re doing it, be sure all the coils and injectors are plugged in to the electrical harness. They’re really hard to see, and reach. I think it could be easy to not get one plugged in all the way.

(I have trust issues with most shops, I have personally witnessed people paying for repairs that didn’t get done)

 

[docraymund]

Looks like you have a vacuum leak. Search vids on how to conduct a smoke test.

 

[harliemae]

If you're not throwing any codes I doubt seriously it could be your coils. Normally when one of those goes out you will get a check engine light that comes on. You mentioned something about the exhaust manifold that definitely can make an engine run rough. Also like someone else was telling you check your air filter and by yourself a can of mass air cleaner do not use carburetor cleaner and clean your mass air sensor and then use carburetor cleaner and clean your throttle body. And if your air filter is bad do not buy a cheap air filter. Not just Ford but other mechanics recommend only replacing your air filter with a Motorcraft filter. Some people say you can get away with a Fram but the other filters Do not sit in the housing correctly. In doing so it's allowing dirt to go past the filter and straight into your engine. Keep this in mind when you clean your throttle body it will take a couple cranks of the key for you to get the engine started and it will run a little rough for about I would say 10 seconds at the most depending on how much carb cleaner was used and how dirty your throttle body really was. Good luck and let us know if you figure it out what happened. A lot of people post questions on here and we give answers and never hear back from them again. I would just like to know if you were able to figure it out.

PS like someone else said also if it's none of the things I mentioned it could be a vacuum leak. Define that just spray carb cleaner all around the back and the sides of your engine while your truck is running. If the RPM changes then you have a vacuum leak.
Again good luck.

 

[Richard Gibbs]

If you already did the coils and plugs it is very likely it's a vacuum leak. If you've never replaced any hoses, I'd say I'm 99.9% right... plus i had the same issue.

 

[BOB4254]

I have the same year and engine.

I had the same issues as you.

This will solve your problem.

My 1998 Expedition runs like new!

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