I bought a 2004 Mazda Rx-8 automatic and when I pressed the gas pedal to the floor it didn't take off fast, it stayed at around 15-20 mph until 2k rpms when it started picking up speed and also made a loud "reving noise" , the car has no check engine light and I feel it's a transmission issue , does anyone know what's wrong with my car and of this is an expensive fix? Thanks

 

Check the fluid level.

 

Verify the condition of the coils, plugs, cat and fuel filter/ pump. Also check the air filter.
As edz mentioned, check your fluid levels.p