In Dutch oven, heat oil over medium heat; fry chorizo, onion, garlic, salt and pepper, stirring occasionally, until onion is softened, about 8 minutes. Stir in tomatoes and vinegar; cook over medium-high heat, stirring occasionally, until slightly thickened and tomatoes are tender, about 15 minutes. Add clams; cover and bring to boil over high heat. Cook just until clams open wide, 8 to 10 minutes. Discard any that do not open. Remove from heat; stir in basil.