Has anyone changed their plugs and had idle go from 400 to 200 rpm causing truck stall at lights? 2004 F-150 5.4.

 

Are all your vacuum connections tight after hooking everything back up? I'm not sure how it pertains to an F150, but I had an old carbureted Chev pickup that would do similar stalling and lower idle due to a loose vacuum line.

 

Have you rechecked all the plugs and COP's to make sure everything is in place correctly. Also what kind of plugs did you go back with?

 

Could try D/C the battery and letting the computer reset too. Who knows if it was doing things to compensate for the old plugs.

 

Vaccuum connections are tight. Mechanic disconnected battery when he changed plugs. I was thinking computer might take some time to re-learn. Also, I'm going to run 93 octane gas and a fuel additive for a couple tankfulls. My truck has 165,000 miles.

 

Fuel filter plugged up? Or worse, fuel pump on its way out? Hopefully not.

 

If it was idling @ 400 rpms before you did the plugs that's pretty low seems like normal should be between 600 and 800 was it idling smooth at 400?

 

Checking ALLDATAdiy.com it shows the factory idle speed should be between 580 and 620 RPMs when hot.

 

Fuel filter is pretty new, besides truck runs fine on e-way or any time it's not in gear at idle. Truck has always idled about 400 rpm and it runs smooth.

 

The 400 rpms still seems low to me I don't know a lot about about the interaction between the PCM and the sensors that control engine idle. I say at 400 rpms you wouldn't have a lot of cushion for a/c compressor kicking in or putting it in gear if it's an automatic trans the engine could stall unless the pcm correct for this and keeps the rpms. Any codes? what are the RPM before it warms up?

 

There are no fault codes. RPMs are ok when cold, progessively worse when warming up. Have to rev up to keep from stalling then. Going to follow TSB for this and have chip flashed.

 

Clean the throttle body. Mine was doing that and it was just a filthy throttle body. I cleaned it without taking it off and it has been fine since I did it.

 

What did you use to clean Throttle Body? How do I get to it. Thanks.

 

Take the air cleaner housing off. Reach in and spray some carb cleaner in the throttle body and wipe it out with a wrag. I held the butterfly open and cleaned the inside of it that way too. You won't believe all the crap you will get out of it.

 

any update on what resolved this? mine is doing this crap now. its annoying as hell. just done plugs, and replaced fuel filter. went to parts store and picked up mass air flow cleaner and carb cleaner and going to do what is stated above.