Karl William Knauz, 38, a manager in his family's auto dealership, Knauz of Lake Forest, a business founded by his grandfather, died Sunday at his Lake Forest home. He was also a commercial pilot with Coleman Aviation in Rockford and a certified flight instructor. He was a graduate of Emery School of Aviation in Greeley, Colo., and of the University of Illinois, where he earned a bachelor's degree in design in 1983. He is survived by his wife, Sydney Duwe Knauz; a son, Alexander; his parents, William and Inge; a brother; and a sister.