That is an access port to pressure test the evaporative emissions system.
The trans in a Dakota is not controlled by vacuum.
Autozone web page has the Vacuum diagram for the1989 Dodge Dakota.
Dodge transmissions do not use vacuum modulators.
Dodge transmissions do not use vacuum modulators.Dodge transmissions do not use vacuum modulators.
No vacuum tubes on the Dakota. It uses electric servos.
You can find a vacuum line diagram for a 1989 Dodge Dakota by checking the owner's manual. You can also find them at different auto part retail stores.
need vacuum system diamram for a 1989 3.9 dodge Dakota p.u.
Check for vacuum leaks.
Try google, your local library, or go to a dodge website, or www. howstuffworks.com
Just pull off the old vacuum hose, cut an appropriate length of the correct sized replacement hose and push it on. If you can't find, or get, the right sized vacuum hose, windshield washer hose is often an acceptable replacement. BTW, it is totally acceptable to replace those hard plastic vacuum lines with rubber vacuum or washer hose.
O2 sensor or vacuum leak
Dodge Dakota was created in 1986.