There is supposed to be a vacuum hose that goes from an air nipple on the air plenum. It's about 1 inch behind where the throttle body bolts to the plenum. That nipple should have a vacuum hose coming off and going to that nipple on the firewall. If you have cruise control, you might have a T-fitting that splits off and goes over to the acuator, as both run off that same vacuum port line.

1995 Trooper LS auto 3.2 DOHC /w SOHC intake
1989 Trooper 2.6 auto
1989 I-Mark RS DOHC 1.6
1991 Stylus XS DOHC 1.8