I've been having a pesky P0174 code and could not find the vacuum leak on my 2004 3.0 xtype. I checked all the major 3 leak candidates and all check out fine. Sad to say I started throwing parts and replaced the O2 sensor for upstream and also replaced the MAF sensor. Those didn't fix it. I finally broke out my homemade paint can smoke machine and did the following:

• The paint can smoker I made using examples off YouTube. For my forced air I use a 12 volt inflator that we have had for years to blow up pool toys and inflatables. It has a small nozzle that works great for the plastic tubing of my smoker device.
• I removed the air cleaner cover and disconnected it from the accordion flex pie that goes into throttle body but left accordion attached to throttle body
• Over the opening of the accordion tube I stretched a latex rubber glove. I cut a very small hole in the tip of the middle finger just big enough to fit my smoke supply tube nozzle.
• I lit some carboard wet with mineral spirits in my paint can smoker and turned on the blower and put the nozzle in that finger opening.
• Very soon I saw smoke coming out from the back of the intake near the firewall.
• When I traced it down I saw it was coming from the rubber boot of the tiny vacuum line that has the red tube covered in a "conduit". That red tube was broken into about two inches from the rubber 90 degree boot where it attaches.
• The part number for that vacuum tube is C2S28870 I see that from some of my older posts that I replaced this same tube back in 2016. Guess in my environment they don't last long

 

Nice job. I did a similar hack looking for a leak in the Evap tubing. Large plastic bottle, pour in mineral oil and UV dye, use a tiki torch wick wrapped in NiChrome wire, dip the wick in the oil & dye mix, put 2 barbed pipe nipples on the lid and screw it on. Bike pump attached to one hose to force air out, long hose on the other to run to wherever the smoke needs to go. Apply a few volts to the NiChrome wire until the oil reaches smoke point and you are off and running. If you can't see visible smoke you will easily see the leak using a UV flashlight. My setup was about $30, a massive expensive compared to yours.