Background:

99' F-150 4.6L V8 very well maintained.
Autolite Platinum Plugs (changed 20k ago)
Cleaned TB (once a year)
Cleaned Maf regularly
Fuel Filter changed regularly...
etc...

Anyways,
Lately since it's been colder my truck has been running rough until it warms up. When I first start it it idles pretty rough but a minute later it runs like a champ. Well, tonight I went to my girlfriends house, truck ran perfect the whole way there. Just now I started it to leave, back out of the driveway, I put it in drive to take off and it just stumbled and sputtered like crazy. It did it the whole way home if I would get above 1/4 throttle. It never died or put out a CEL, I even gave it the "Italian Tune-up" to see what would happen. It stumbled more but never gave me a CEL or died. I clean my IAC pretty regularly but Ive been noticing more and more that I have to clean it in shorter intervals before it starts running rough again. It has never run this rough, especially without a CEL. I'm going to check IAC in the morning along with the MAF (even though that normally throws a code). Do you think it could be my PCV as well? I was going to change it a couple days ago but I had to have one ordered from O'reily, should be in now.

F.Y.I. it idles pretty rough as well but it's not idling high, so I know its not a vacuum leak right?

Thanks a lot everyone.

 

put in some Motorcraft Plugs

 

I have to agree with that.
The Motorcraft plugs work best in thees trucks!

Phil

 

Bad plugs would cause CEL right?

 

normally yes. it might not have had a time to set it yet. drive it around a see if the light comes on

 

I did, i drove 10 miles. No CEL...its not a misfire, plugs are fine. Doesn't feel like a miss, just feels like its choking out. Ive had a misfire before and it feels sort of the same, but a lot worse. Like half my cylinders arent firing. No way 3 or 4 of my plugs went out at once. Thanks

 

hmm...could be some clogged injectors

 

But just out of the blue like that? It ran fine one minute, then like hell the next.

 

EGR might need cleaning Put a hand vacuum pump on the vacuum port on top of the EGR and apply vacuum while its running to see if it idles different. If the idle doesn't change the EGR needs attention.

 

Plug change fixed the same troubles in my 4.6. Autolites are junk man. Use motorcraft and see if it doesn't fix it.

 

Bad gas maybe?

 

A couple of things come to my mind...
1. Yes, clean the EGR valve
2. Clean the IAC
3. I would replace (just for the heck of it) the temp sensor unit- it might have become "lazy" creating an over rich mixture especially during cold weather.
4. Of course, you have checked the air filter

 

Fired it up this morning and it ran just fine? Crazy...

EGR valve is pretty new.
IAC is cleaned regularly.
I just cleaned/oiled my K&N filter during my last oil change (2k ago).


Going to buy a new PCV valve to put in for the heck of it.

 

Well crap..

Ran fine the whole way to the store, started it up, on the way home it started sputtering again. This SUCKS!

Looks like it only does it after it reaches operating temperature? Its not running any hotter than normal either.

 

Clean the MAF.