This is a common problem when using the polyurethane bushings. Contradictory to what you may think the bushing is supposed to do, it actually has too much give too it over the OEM bushing and causing an unstable feeling. The rear end of front wheel drive honda/acuras is fairly simple and put together well from the factory. Springs/struts & a camber kit back there is all you should ever really do. Once you starting fucking w/it and replacing little things, is usually when it starts to become symptomatic.