Did you introduce them slowly, or just put them together in the house?
I am sure that your chi feels threatened by the presence of another adult dog, while the yorkie probably feels the need to assert himself in the new house among your chihuahua.
My only suggestion would be to keep your yorkie kenneled as you would a puppy, introducing him to the chihuahua frequently with your direct supervision. Bring out toys and holding your yorkie (since it seems he is the aggressor from your post), you can bring them closer and closer together, petting them to keep them calm and collected, and try to play with them with their toys. It might take a while to get them accustomed to each other, and your "introduction" times might be short at first, but I would hope that with time they would eventually warm up to each other and spend more and more time together without fighting, even if they just learn to coexist rathen than being best friends.
Good luck and keep us posted! |