In 1088, he spoke on the request of Bishop Henry of Verdun to end a conflict in the Abbey of St. Truiden where the bishop and emperor Henry IV had both appointed a successor abbot. As a result of his diplomacy, the emperor transferred the authority of the abbey of Sint-Truiden from Henry I, Duke of Lower Lorraine, to Arnold. Arnold forced Henry and his ally Godfrey of Bouillon, to withdraw from the monastery. The domain of Arnold expanded with the County of Rieneck by his marriage to Agnes.
Arnold married Agnes von Mainz, daughter of Gerhard I, Count of Rieneck, and Helwig von Bliescastel. Sources disagree on their number of children, but are believed to include:
While the confusion about the non-existent "Gerard" remains, Arnold is now understood to have been succeeded by his son Arnold as Count of Looz upon his death.