I have a 5.4 24v engine in my 2004 F-150 that has a humming noise sometimes when I slowly accelerate. It sounds like a four barrel carb kicking in but no extra power. If I let off and accelerate again it works fine. If I push the peddle down farther it passes and accelerates fine. I have cleaned the MAF sensor with spray cleaner no change. I pulled the throttle and spacer off and cleaned with no change. Sometimes the engine will increase 200 RPM's and back to normal over and over again(8 to 10 times). Any ideas before I throw in the towel..

 

Idle air control valve maybe. They tend to make a little noise when theyre stuck open, and the idle will fluctuate. Could also be a vacuum leak of some sort. Any check engine light?

 

04's dont have an IAC - electronic throttle.

 

Thanks. Now I know why could not find it. I checked for vacuum leaks but did not find any. No engine light or stalling just a flat spot with a humming noise when I accelerate slowly.

 

How many miles on it and what's the maintenance history?

 

96000 mile has been well maintained. All fluids maintained and changed, injectors cleaned, but I have not changed the plugs. I was leaning to the MAF or throttle sensor.

 

96k? Plugs are overdue. Ford's current recommendation on 3v plugs is 60k.

 

Changed Plugs. $400. No change. Also replaced the throttle sencer. No change. Sometimes has a bucking when I let off the gas on the Interstate

 

Could be a COP starting to go bad

 

400 for plugs!?!? Dang i got a nice set for like 30 bucks and spent a few hours in the garage.

 

Sad but I have to ask what is a COP

 

No worries bud, Coil over plug... it is what these truck have instead of plug wires