I purchased a 91 mustang GT with one of these installed. As best I can tell the bottom end of the motor is stock, (it might have an E-303 cam), but I'm not sure. I am having an issue with the car surging once you let off of the gas and it takes a little bit for the RPM's to come back down. What do i need to do to correct this, besides take it off. I have already removed the 70mm throttle body and the 30lb injectors the guy had put in and it helped but the car is still not running right.