Guys,
you have helped me in the past with my 99 f150 4.6. I just stepped up and bought a 2003 lariat FX4. It has 40,000 miles on it. It runs rough at idle at times. No light. Any suggestions?
Joe

 

I would say start with cleaning the IAC.

 

my 03 fx4 idles rough when i run low grade fuel (85.5) but if i run 93 or mid grade it idles smooth. my mom's navigator with a 5.4 is the same way.

 

You should be running at least 87 octane, and unless you have a tuner that requires 93 octane, there's no reason to run a higher octane than 87.

 

My 01 5.4 is the same way. It seems very picky about fuel quality. It will just seem like its running rough,not misfiring, but not smooth. Mine has 50,000 miles on it. I have noticed that when it starts running rough I can add a can of Seafoam fuel treatment and it will smooth it right up so I know its a fuel quality issue. I have tried fuels from different stations and brands and its never with consistent with any particular brand. The damn thing is just picky thats all I can say.

 

I've got an 04 scab 5.4L that also idles rough. Always has and dealer said it's normal. Good luck.

 

hmmm... my chevy breaks down on the side of the road all the time; always has...... But the dealer said it was normal so..... it's all good.

 

had exact problem , the problem is in the egr valve four dealers could not find codes they all said it was normal to idle like s**t sometimes ok most times when at stop and warm it felt like bad miss

 

Had that problem like that with my 97 5.4 F-150 SC turns out it was an oxygen sensor. Lived with it for 60k with no CEL. Only found problem when it finally threw a CEL.

 

Interesting to find out what was the issue with the EGR. Did you replace the valvle, clean it?
Also, I wonder if i'm due for new O2s at 75K.
I have had a starting issue that occurs 1 out every 10 or so times. I'm thinking it is one of the coils( I was planning on pulling each one and checking resistance). But also at times, and the wife called this morning, it will crank up and run rough then smooth out. I could see how maybe it could be an egr open a little, but just guessing. Of course no codes ever. This is on our 2000 5.4L Expy w/ only 75K. 93oct programer, efans, kn and 3" exh. No other mods.

Appreciate any feedback.

Rob
Humble,TX

 

check the pcv tube and see if u have a vacuum leak...u should be able to hear the hissing noise when u open the hood but if not i would check that...

 

I think before I start tearing apart my 00' 5.4, I'll try the higher octane. I've been pouring system cleaners down it's throat constantly with absolutely no change. I asked a mechanic about the O2 sensors, and I'd need to take out a loan to get a shop to replace em. I was also told by a mechanic that O2 sensors rarely actually need to be replaced ( ). As far as cleaning the EGR, easier said than done on mine.