Well according to http://ark.intel.com/products/75047/Intel-Core-i5-4670-Processor-6M-Cache-up-to-3_80-GHz your CPU supports AVX2. Have you tried one of the other mining binaries? Have you tried to benchmark scrypt without doing any actual mining?

Perhaps you've got a program on your machine interfering with the miner, or your hardware is a bit wonky or you've found a bug in the miner causing by your parameters.