Gavin,
The Mishimoto Intake is designed to be a bolt on part with small HP and TQ gains so that customers are not required to tune their cars. I apologize that you are not happy with the performance of the Mishimoto Cold Air Intake and it did not perform up to your standards.
Mishimoto does offer a life time warranty for their products if you believe the intake is defective or not performing as it was designed we would recommend that you reach out directly to Mishimoto (contact info noted below) and explain the issues you are having with the product and they can begin to troubleshoot and action a result if necessary!
Contact Page: https://www.mishimoto.com/contact/
Regards,