I used to have problems with buildup and itchy scalp, too, when I was using the cheaper products like Suave and VO5 cowashes, and LA Looks and LaBella gels.
I could never pin point it down to a single ingredient, so I recommend trying some products with higher quality ingredients. I eventually started using Deva One-C to massage my scalp, and mixing it with a thick protein dense conditioner for the ends. From time to time, if I start to feel extra oily, I use Deva No-poo to cleanse. I'm sure ACV/BS would do the trick in place of No-poo, tho.
CG since 8/21/12
3B, Fine, Low-Med Density, Low Porosity, Normal Elasticity (I think...)
I love henna!
Poo: Shampoo Bar
Co-Wash: Yes to Cucumbers
LI: Innsersense Organic Beauty Sweet Spirit
Styler: Alba Botanica Strong Hold Gel
check out my blog for more info about my styling routine @ http://killthebananas.blogspot.com/