I have an 04 F 150 with a 5.4. It has a very slow (5-600rpm) and rough idle once it reaches full operating temperature. What can I do to alleviate this problem?

 

The Intake Air Controler (IAC) is not being controlled by the computer.
Stuck, gummy, faulty etc.
This device controls idle speed by controlling air bypassing around the throttle plate.
Right now it's closed and your running on the air getting by the throttle plate's min stop setting. Never try to change plate stop setting to correct a fault.

 

Are you throwing any codes? If you are throwing both P0171 and 174, it is likely you have a vaccuum leak.

I just got done with my own 97 5.4 with 203K on it. It would run fast when driving, always around 1500 RPM or so. Then when you came to a stop, or put in Park, it would idle down, and nearly die. Very rough idle. Turned out it was the rear elbow on the PCV hose. It was suggested here to look for that, and by-gosh, JBrew and others were right on!

 

Mine idles at about 550-600 when it's fully warmed up and the truck vibrates a bit but it sounds like a smooth idle when I get out and listen to it. It has a TINY bit of lope so it's like RrrRrrRrrRrr. If that makes any sense haha.

 

What can I do about the Intake Air Controler (IAC) issue? Does it need to be replaced or do I need to clean up the "stuck, gummy" area? I am not showing any codes.

 

Does an 04 even have an IAC? I thought it was drive by wire.

 

can I get that pcv elbow at autozone? The dealer only sells the whole line...

 

What's up? You find a leak? I noticed you posting here and their- Need a hand ?

Well , you should be able to buy just the elbow, at least you use to be able to. It may depend upon who you talk to in the parts department. Try another dealership if you have to.

I'm not sure this is the one you need, but this part number should get you close.



Also , with a 97 , it may be a good idea to replace the entire PCV system. There's really not much to it . If I remember right , it's about $30. What happens over time is the hard line dries out and fractures/cracks which can be hard to detect. But, yea, that 90 degree elbow is the most common problem.

Here's a pic of a 98 PCV system complete . Yours should be similar.



Here's another pic of a complete system with the insulator cover wrapped around it. -



With lean codes, this is the first area you want to thoroughly check. Feel free to use my gallery for other pics/diagrams by clicking on the little camera upper right hand corner of this post.

 

yeah I ended up buying the whole line for 39 bucks but at least it came with the pcv valve
thanks a ton btw

 

No problem

 

yup i got to do this now i just cant get my big *** arm and hand back to it!

 

mine is fine then the idle will drop/stumble for about 5 sec then go back to normal for a few secs then do it again!

 

Just fixed mine! Well my PCV elbow was the problem it was in bad shape. It came off in 2 pieces. Went to parts store 10$ later truck is running like a new truck But man it was hard to get my hand to the back of the intake manifold!!!