Just moved to florida from south dakota. I was using 5w-20 up in the colder south dakota and now since i have moved, i haved noticed a difference in the idle. Should i change to a 5w-30 since it is much hotter and more humid?

 

That would be a good start.
Mazda does recommend 5W20 but they also say use whats best for your environment so if it's HOT where you drive use a heavier grade. Here is what the manual says..........

Engine oil viscosity, or thickness, has an
effect on fuel economy and cold-weather
operation (starting and oil flow).
Low-viscosity engine oils can provide
improved fuel economy and cold-weather
performance.
But high-temperature weather conditions
require higher-viscosity engine oils for
satisfactory lubrication.

 

This could also be related to your ignition system. What year is your RX8? When's the last time you changed the plugs?

 

5w30 is definitely where you want to be at if not a tad heavier, especially in a climate like Florida.

 

Thanks guys, Its a 2004 with only 28,678 miles and i changed the plugs like 5k ago somewhere around there i think.

 

im running 10w30 here in AL... works wonderfully

 

I just made the switch to 5w-30 from 5w-20 Didn't notice any change in idle or performance by doing so. When was the last time you replaced plug wires and coils?