Clean your Mass Airflow Sensor with some MAF sensor cleaner or contact cleaner
vacum leaks around intake
Inspect your intake hoses and make sure non are leaking
Inspect also the vacuum caps on the manifold and make sure they are both on
dirty eccentric shaft sensor
Check if your eccentric shaft sensor is excessively dirty and clean it
Check that they are perfectly clicked in place and in the correct order.
If your coils, wires or spark plugs are older than 4 or 5 years, It's a good Idea to replace them.
More power + better mpg
Sometimes is just an ECU error, and all you need to do is reset it by:
1) turn ignition on, but not the car
2) pump your brake 25 times fast and hard until the oil gauge bounces (it does not bounce on all models)
3) Ignition off, ignition on and start the car
Do a compression test and if you have less than 5 BAR consider rebuilding your engine.
Malfunctioning throttle body
Inspect & clean your throttle body if necessary and make sure it's working properly.
Low quality fuel
If you use low quality and octane fuel, you're gonna have a lot of issues down the road in the long term.
Premium is the best gas for the Rx8.
Minimum Octanes to put inside is:
- EU Ron 95 octane
- US 91 octane
Optimal : 98/100 ron octanes
Clogged catalytic converter
The catalytic converter can be full of debris that accumulates over time.
To solve this, you can try cleaning it with a special catalytic converter cleaner or better, buy a new one.