Tesla is expected to introduce an all-wheel drive version of its Model S sedan, according to a source familiar with the matter. Tesla calls this feature “dual motor,” which may answer what Chief Executive Elon Musk was referring to in a cryptic tweet last week. The Palo Alto, Calif., electric car maker’s co-founder posted an image of a vehicle partially obscured by an opening garage door, alongside the date Oct. 9 and the tease: “About to unveil the D and something else.” The Verge first reported last summer that the company was working on all-wheel drive for its sedan and in recent days several sites posted pictures showing an AWD “P85D” version of the vehicle, including AutoBlog. A handful of analysts are also predicting an all-wheel drive variant. The feature could help lure new customers in regions that suffer through long bouts of cold and wet weather, including the Northeast and Canada, where Tesla sales have been relatively soft.