I have an 04 6 speed rx8 and I only get about 200 miles to a tank, that’s if I’m trying to get the best mileage possible. Anyone know what may be wrong or how to fix this problem?

 

Ignition coils, spark plugs, wires could be one cause. The stock coils need to be replaced every 30k miles or so.

Clogged catalytic converter could do it as well, check if it glows red after a spirited drive.

Bad coils often lead to clogged catalytic converters, which lead to dead engines, so if you haven't addressed those components in a long time, start there and don't wait.