^^^ If you are trying to identify a vacuum leak without a vacuum gauge, and you have a hand held programmer with ability to datalog short term and long term fuel trims you may be able to tell this way. Observe that LTFT's with the car idling. If there is a vacuum leak you have unmetered air. So the car will want to run lean. The ECM will see this and try to correct for it by adding fuel which can be seen in the STFT's and especially LTFT's. When you increase the throttle vacuum decreases (moves toward 0" Hg). As it does the trims will then correct again because the ECM will see AFR getting richer as the air coming in seeks the lesser route of resistance (TB is opening so engine is seenig more metered air) because the vacuum leak becomes less as throttle position gets closer to WOT. Ford describes this basic technique in their shop manuals.

Check the link out. Its for a 2005+ but it still tuning basics 101 troubleshooting for most modern day fuel injected cars.

https://iihs.net/fsm/?d=8&f=Adaptive...niques.pdf&p=1

Hope this helps.