87 octane? IIRC, they need at least 91. It's because of the continuously variable timing control. And any OBD II car is going to have "warning lights." The only way to avoid the SES light on that car after a header/cat swap is with a o2 simulator. THEN you won't have warning lights.

Lemme know if you need any help modding it, I've had a Spec V since 2002.