Vacuum Leak
 

Hello. New member. 2001 Super Crew with 5.4l engine. I have an audible vacuum leak but only after it sits overnight. Vacuum leak goes away within 10 minutes of driving. During this time, the idle is very erratic. I was finally able to get the leak to change pitch by wiggling the #8 spark plug coil/boot. I have tried wiggling, touching everything under the hood. I have squirted WD-40 at areas that I suspected. Spraying the #8 plug hole will change the idle, but only during warm-up. Once the engine has been run for more than 10 minutes, it runs fine the rest of the day, even after sitting in the parking lot at work all day. Any ideas? Thanks. Bret

Changing the intake manifold gaskets took care of this problem. It was not the dreaded elbow or the IAC valve. This video walks you through the job.

Thanks for posting your solution. Nice work.