Hesitation and/or a lack of power can be caused by the secondary shutter valve (SSV) in the intake manifold becoming stuck open due to carbon build up around the SSV shaft. This may occur with no Check Engine light illumination but eventually the light will illuminate with code P2070 (Secondary Shutter Valve [SSV] stuck open). The cleaning procedure described under the service bulletin is a long process and it is recommended to install the updated SSV actuator and gaskets. The SSV is activated at higher RPM and the carbon accumulation can happen when it opens infrequently. The effects RX-8's built before April 18, 2007.
2006 Mazda RX-8 Problem Reports
RepairPal Verified 2006 Mazda RX-8 Problem Reports
Some models may have a problem where the Check Engine light illuminates indicating an improperly tightened fuel cap. Due to improperly manufactured threads on the fuel filler pipe, the filler pipe may need to be replaced.
If the climate control's heat/cold knob is not adjusting to the desired temperature, a new climate control unit may be needed.
Be sure to check your owner's manual and use the correct engine oil. Mazda does not recommend using synthetic oil in the RX-8's rotary engine.