I noticed that on my ‘05 5.4 that the half shafts both turn while in 2wd. I got on her and did some research and found a post that explained very well how to find the problem. From that, I found out that my solenoid was bad (got water in it, of course) so I replaced that and now my truck will go into 4hi and low. Awesome. But the half shafts are still spinning while in 2wd. So I got a vacuum pump and checked both IWE’s and both of them disengaged with only about 7psi. But when I have the truck running with all vacuum lines connected as normal and front end raised, it seems that there isn’t enough or any vacuum which is leading me to believe there is a vacuum leak somewhere. My question is, what’s the easiest way, for an average guy with average tools, to find out where the leak is at, short of checking the entire line visually?

TL;DR: checked IWE System, suspect a vacuum leak in the line somewhere, how do I find the leak?.. easily

 

Get an UNLIT propane torch and wave it around the lines. If you get a change in idle speed, you've found your problem.

 

The computer is usually too fast for enrichment methods to cause a noticeable change in idle speed. Usually, you have to use a scan tool to monitor either short term fuel trims or the upstream O2 sensor voltages to see the response.
Cap off sections of the lines to divide the system.