Grease a large baking sheet; set aside. In a medium saucepan combine the 1 cup water and 1/2 cup butter or margarine. Bring to boiling. Add flour all at once, stirring vigorously. Cook and stir till mixture forms a ball that does not separate. Remove from heat. Cool for 10 minutes. Add eggs, one at a time, beating well after each addition till smooth.
Spoon dough into a decorating bag fitted with a large plain round tip (about 1/2-inch opening). Pipe 10 to 12 strips of dough, about 3 inches apart, onto the prepared baking sheet, making each strip about 4 inches long, 1 inch wide, and 3/4 inch thigh.
Bake in a 400 degree F oven about 40 minutes or until golden brown. Remove and cool on a wire rack. Cut éclairs in half lengthwise and remove soft dough from centers. Fill bottom halves with ice cream; replace tops. Cover and freeze till serving time. To serve, remove from freezer and let stand about 15 minutes to soften.
Meanwhile, for sauce, in a medium saucepan combine the 1-1/2 cups cold water, cornstarch, and coffee crystals. Stir in corn syrup. Cook and stir till thickened and bubbly. Cook and stir for 2 minutes more. Remove from heat. Add the 2 tablespoons butter or margarine and vanilla; stir till butter is melted.
Serve some of the warm sauce over éclairs. If desired, sprinkle with pecans. (Cover and chill any leftover sauce up to 1 week. Reheat sauce and serve with ice cream.) Makes 10 to 12 eclairs.