I have encountered a vacuum problem while doing an engine swap from 1995 3.9 Liter V6 automatic with a 1996 version that used to have a manual transmission. The engine turns but would sputter at idle then dies out. I have a good feeling that it's got something to do with the vacuum lines being mixed up or unhooked. However, I need a vacuum line diagram to check this hypothesis of mine.
On the automatic transmissions there is a vaccum line usually on the top of the transmission and needs to be hooked up, usually this only effects the shifting though. You should go to you automotive store and ask for a Haynes automotive book referring to your year model and make of you vehicle. In the book it should have a diagram. If not there also books sold that are specfically for vaccum line diagrams.
Were can I fine diagram for 1999 dodge Dakota 3.9 cyl vacuum system