budedm

My 2001 5.4L does this every year and I'd like to get to the bottom of it. When the temp gets below 20 degrees, the idle becomes erratic. Almost like it wants to stall but it doesn't. It isn't a low idle, it is 500-700 but it varies and misses. It does this even after the engine is completely warm, like on a 30 miles drive. I come to a red light and it sounds and feels like crap. I'm thinking it has to be in the air intake somewhere because that's the only place any cold air is. Anyone have any ideas? I have replaced the IAC valve, the EGR, and cleaned the MAF sensor.

budedm

Nobody has any ideas to help me?

budedm

Well, I put some dry gas in the tank. Still no help. Anyone?

Martian

Moved to 1997-2003.

mandingo32

Look for holes or cracks in the elbow of the PCV valve. Mine started idling rough in colder temps. I found a hole in the elbow of the assembly, replaced it and haven't had a problem with the idle since.

RCButler

Yep....check the PCV hose for cracks and/or holes. It's a common problem in older, high mileage modular engines. Just replaced mine (2002 4.6L, 138k miles), had a hole big enough to stick the end of my pinky in. It was doing the same thing.

If that's not it check the remaining vacuum lines.

FL_F150

The elbow he is talking about is the one at the back / top behind the carb. Mine had a hole burnt through it.
Made a you tube video about it billmcgraw1959 is the name i use

Tackle

Mine was doing the same occasionally. Ended up being intake gaskets at 140k.

FL_F150

Update?

Jbrew

I guess yuh figured it out ehh ? Since you went MIA after posting, -not very respectful to those attempting to help. Never the the less, you posted the important info that makes the problem easier to pinpoint.
When it's that cold it doesn't matter new or old IAC, they can still ice up if the engine didn't come with the cold climate system. You don't have a unmetered PCV or intake leak, that's where the rpms come into play. A unmetered air leak will cause higher rpms always, never lower. The factory program is 700-750. A system tight intake and PCV will be right at 730 rpms at warm idle in park. That's how you disquisition a vacuum/intake leak issue with these particular trucks. Anything below that is indicates restriction within the system or IAC.
With that in mind the problem is the IAC or PCV valve. Reasons for it, - blow by which naturally occurs within a combustion engine has become excessive due to weather (cold climate). IF you drive the vehicle short distances the blow by (moisture) doesn't have the time to cook off and builds under the valve covers. IF your using anything other than a Motorcraft PCV valve, then the problem can be 10 times worse because no one 3rd party produces a PCV valve with the proper margins other than Motorcraft. They are all too tight and the engine won't breath properly. That's been proven in the past. It's not noticed so much in warm weather but long term that little valve can cause an early death. So either your using a 3rd party valve that keeps icing up or too many short trips is causing excessive blow by and icing up the IAC. And if the truck doesn't have the cold climate system, this can take a little while to thaw out during the drive cycle. Pretty much the most common reason for this to occur. This is more problematic with the 5fours because of the IAC location right behind the TB elbow where as the 4six is on the other side of the TB and gets it's heat from both sides of the engine.