Hey guys, I noticed today that there is a very subtle sort of whistle at idle. The lightest feather on the throttle makes the whistle go away. The truck is an 05 king ranch, with a 5.4 L. Any one ever notice anything like this? I sort of tinkered with the plastic intake system and did not notice any change in the sound. The truck idle and runs excellent, just wondering about this sound. Let me know what you think..

 

You have a vacuum leak. Get a spray bottle of water and spray the lines slowly with the engine running. When it stops for a second you found it. Ifound mine like that It was on a vac line by the battery. I guess some acid got on it. Their are other possibilities for the noise but that is No.1

 

Amen on the leak. I have had to troubleshoot leaks twice on a 99 150. One was a 90 degree boot under the intake and the other was a 90 degree boot on the back passenger side of the intake. Not neccessarily the smartest thing, however I found both by letting the engine idle and with gloves, I began lightly grabbing and moving every line I could find. I ended up finding the problem rather quickly.

Oh, if you your engine light comes on and after you have the computer read it shows to be an O2 sensor, it likely is a vacum leak from somewhere around the intake. That is what started the process in the beginning for me.

 

Spray ether all around your vacuum lines. The engine will rev up when you find the leak.