I am having the same trouble with my Luca Dean, but he was a bit malnourished. We've been giving him a vitamin E and a teaspoon of olive oil a day, but he still doesn't 'shine.' He's about 5 months and still has his "puppy coat" though. Anyone got any other suggestions, or should I ride it out until he has grown more hair?
Some yorkies do end up with a "cottony" or "wooly" coat ... and, unfortunately, never grow the silky shiny coat that yorkies are known for. Here's an article I read about how to care for a non-silky coat:
http://members.cox.net/jrogan/care.html
She has included in the article how to tell what type of coat your yorkie has, and also how to care for the variety of coats. The music is not to my liking though.
BTW, I use Miracle Coat spray and shampoo on Dean. Used Pantene conditioner for a while, and that was okay, but I read somewhere there's the buildup issue which can really dull a thin-haired or puppy coat. I use Hylyt on my other dogs and that works fine for them, but idd nothing spectacular for a yorkie coat. It is non-soapy though, and can be used as often as necessary.