first off
what kind of engine is in the car, they made two in 1992 :a:

before doing anything else, top off your coolant tank/radiator and then warm up the car. carefully open the bleed hole on the top of the thermostat housing, near the throttle body. bleed any air out of the system. air in that area can affect the sensor and cause erratic idle.

its most likely sensor or vacuum related so if you take it somewhere they will probably fix it in 10 minutes and rape you on price since its a lude.

~boom