Dog barking at other dogs help?

Hi i recently just acquired a little 1 year old chihuahua when i went to get him he was a little scared as the lady who had him before had 5 kids and i think they played rough with him. He basically lived in a handbag lol he never got out and if he did he was carried or in a bag so he never really got socialised now my problem is whenever i take him out he barks non stop at other dogs all the time non stop except when we have walked a gd distance away and no dogs are near he is fine hes not aggressive just barks and pulls towards the other dog i think it maybe fear more than anything weirdly enough he never barks at another chihuahua how can i resolve this as its very annoying when he barks non stop at other dogs i also have another chihuahua at home and he is fine with him just dogs outside??? any help appreciated thanks