Engine stalling/stumbling problems can be caused by a failing mass airflow sensor.
Car Problem Reports
Volvo 780 Engine Stalling Due to Mass Airflow Sensor Failure
Volvo 780 Problem
Engine Affected: 2.3L 4 Cylinder Turbo
Visitor, 1990 Volvo 780, 2.3L 4 Cylinder Turbo, 247,000 mi
fixed warped head. drove car at speeds of 70miles hr.after 15min car backedfire, checked timming,pressure,replaced mass airflow sensor. car starts but no power