I recently bought a 05 4.6 XLT with 14,xxx miles. I've driven about 5 thousand miles and have noticed a rough idle once warmed up. Like it has a miss? In those 5 thousand miles I replaced the plugs(motorcraft), coils(Accels), factory fuel filter, and added a drop in K&N air filter. Now I'm not to sure what direction to go? The original owner traded it in at age 92 so it wasn't driven much.Still on original factory tires. Any ideas would be greatly appreciated!

 

My wife's 04 4.6 Expedition developed a miss. Seems I recall a thorough throttle body cleaning that removed a build up. I cant remember what it was called.

It builds up a bunch of gunk, once cleaned it ran like a scalded dog!

So my point is, have you thoroughly cleaned the throttle body?

 

1. Get any/all codes pulled -including stored Pending codes. Mode $06 misfire data?
2. Accels are a crapshoot.
3. Clean MAF
4. Clean TB
5. Which plugs were used?
6. Was dielectric used?
7. New boots & springs used?
8. Get injectors checked for leakage
9. ....
10. ....
11. ....

MGD

 

No codes. I did my research and got the better of the motorcraft plugs. It had the miss with factory coils to. I replaced each one and started the motor after each on to see what cylinder was misfiring. I have not cleaned the mass air flow or throttle body yet. When replacing the coils I replaced boots and springs.

 

I had the same problem with my '08 4.6. Get some MAF sensor cleaner, it does make a difference. I did everything you did except the coils, then cleaned the TB and MAF sensor. All of that helped. Then I filled up with 93 octane, added 2 big bottles of Techron and some Marine Stabil and drove it down to 1/4 tank before I refilled and added 1 more bottle of Techron for good measure. That seemed to do the trick. My idle jumped from 540rpm up to about 650-660 and smoothed out nicely.

 

14K on an 05? Wow, you scored!

I recently bought an '07 4.6 with 101K. It had a bit of a slight stumble at idle; not all the time. After about 3 to 4 tankfuls of Shell, and one bottle of Techron, it went away.

I'll second (or third, or forth) the recommendation of cleaning the TB plate. I think the changing of plugs and CAPS was overkill with only 14K original miles. I hope you kept the Motorcraft COPS, as I'm betting they are still good, and those OEM CAPS are not cheap!

 

With it idling you can disconnect each coil one-at-a-time to see which cylinder is your culprit. It's probably a sticky injector or dirt in TB or MAP.

 

Yeah stock coils are laying around in the garage. I just filled up with 91 octane and planned on doing a injector/fuel system treatment. Looks like I'll be pulling apart the mass and TB apart and start cleaning. Pretty sure there's a sticky on how to do it in the search engine.



With 2.5 HBS leveling kit

 

Make sure you use Techron and not the other stuff. I usually don't say that, but any of the other crap I tried for the F-150 didn't help at all. We have large fuel tanks, so use 2 of the large 20oz bottles. Go to Advance Auto's website and order them on-line for in store pickup, they are a lot cheaper like that right now.

 

Well I took everyone's advise and cleaned TB and mass air flow sensor. Still has the miss. Guessing it's fuel at the end of the day. So I bought the chevron fuel cleaner. Only did the 1 20oz bottle. Funds are tight. Guess I'll wait a week or two before I report back with any concerns. It'll take that long to burn a half tank...