What might be the diagnostic codes for a shuddering or stuttering at idle while stopped? For example, while sitting at a traffic light, the engine will drop idle speed but then idle up. These idle speeds usually happen between 400-700 rpm while stopped at red traffic light or under braking at idle. Typically the shuddering happens when cold or at normal temp.

 

It's a characteristic of these cars, probably due to the high compression I'd imagine. I threw in Shell 93 octane a few times in a row on my girlfriend's CX-5 with the naturally aspirated engine and the car didn"t do it while also running noticeably smoother. My CX-5 with the turbo doesn't have the vibrations, but the RPM will occasionally fluctate when stopped or idle as well since it's the same motor. Ultimately I wouldn't worry about it. Maybe try a tank with 91+ octane and see if it goes away, but Mazda mainly recommends premium gas for towing with a naturally aspirated motor.

 

If you are not getting a check engine light then as stated by the last response it is pretty much normal.