Place potatoes in a Dutch oven, and cover with cold water; bring to a boil. Cook potatoes 30 minutes or until tender; drain and cool. Peel potatoes and cut into 1-inch cubes.
Combine potatoes and onion in a large bowl; toss gently. Combine sour cream and next 5 ingredients in a separate bowl. Spoon sour cream mixture over cooled potato mixture; toss gently to coat. Cover and chill 8 hours.