Bring a large pot of lightly salted water to a boil. Add egg noodles and cook for 8 to 10 minutes, or until al dente; drain and rinse under hot water.
In a large skillet, brown the round steak pieces with the onion to desired doneness.
In a slow cooker, combine the soup, 2 2/3 cup (or 2 soup cans) of water, sour cream and steak sauce. Mix until smooth. Add cooked steak pieces, onions and cooked noodles. Cook on low for 2 hours, or to desired taste and consistency.