What is "idle tuning?"
Idle tuning is to tune the idling RPM when the car wasn't moving, slowing down and etc. The original idling RPM is 500 to 550 which is too low and it causes a lot of shaking and vibrations when the car slows down or when the car is not moving especially at traffic lights. The tuning will increases the idling RPM to 700 which eliminates the shaking or vibrations from the car.

So what's wrong with the shaking and vibrations?
Very uncomfortable for the main reason. Secondly, strong shaking and vibration is bad for the engine mounting (replacing it could cost 1-2k or at least that's the amount I heard) - same goes to i-Stop as the constant start stops also causes a lot of shaking and vibration (I have no solid proof for this so it's up to what you believe).

What's the process?
It's a very simple process. The guy will connects the OBD cable to the car and then laptop, opens up Mazda utility software and starts reading - which leads to around 30 minutes. Then the tuning actually takes only 5 minutes to change the original value to desire value (500 or 550 to 700). Then it'll take another 10-20 minutes to write back to the car.

How much does it cost and does it void warranty?
The cost is only 150 bucks. Well it does certainly void warranty if found out but since any plug and play also void warranty, I guess it should not be a big problem. I was told there's no backlog or data change log to proof that idle RPM has been tuned and if you want to be safe, you can always find the guy and ask him to reverse back the changes.

How is it now?
So far so good. No more violent shaking and vibrations when I slows down or when my car was on static waiting at traffic lights. The idling RPM will constantly be at 700. Will continue to monitor further.

What's next?
If all is good, maybe by end of the year I'll go for the Stage 1 or Stage 2 ECU tuning to see if it helps in throttle lag, smoother gear change and better pick up response and performance.