:/ I've known a stock miata that did better than 30 mpg...but maybe she drove a bit slower...

I'm really hesitant to modify this car if I cant figure this out...

 

Ditch the stupid pre-cat system...and give California the middle finger for it. Get a 01-05 exhaust manifold for now. You only need a main converter under the car. Swap out the ECU for a Federal one while you're at it.

 

I plan on ditching it and getting a nice turbo-ready ecu. Til then, I want to make sure my engine isn't doing all this damage of its own accord.

 

I've been told to stop it from throwing a code, you just need to move the second O2 sensor further back behind the main cat. It doesn't see a change across the pre-cat, so it throws the code.

But I agree that ditching it completely is the way to go. It's not needed to pass a sniffer test once the car is warmed up. (at least every two years when I get mine through, it passes no problem)

I'm not sure it's worth my effort to swap it until I get a turbo on the car.