Toyota kept the title of world's biggest automaker on Thursday with first-quarter sales of 2.52 million vehicles globally, outpacing Volkswagen and General Motors, despite weakening demand at home. The Japanese giant's numbers, down 2.5 percent from a year ago, come after the German automaker earlier said it moved 2.49 million vehicles in the quarter, while US-based GM shifted 2.4 million units, both up from a year earlier.