security indicator light + MAF issue
 

I have a Mazda6 v4 manual car. Since last month, the security indicator light sometimes came up (stable) and turn off in seconds, when I start to move my car. After 2 days, misfire happened several times, and I felt the car was obviously lack of power when I turn up gear and try to speed up. I brought my car to Mazda dealer, they cleaned Mass Air Flow sensor, but the problem was still there. Then, they reset my computer system, the problem was gone for couple hours. But my car was shaking sometime and misfire happened if I did not step my gas harder. Finally, the dealer replaced the Mass Air Flow sensor and reset the computer system. They did that because they said the check engine light was on (I didn't see it myself) and the code indicated them that the MAF sensor needed to be replaced. After that, I felt everything was fine, except the car still a little bit lack of power.
One day after, the security indicator light turns on again when I try to move my car. (only in case the speed is very low) Once, the light turned on even in case I stop my car with only my engine runs. I can feel the car was shaking at that moment. Also, when I waiting a traffic light, the car misfired again when I tried to move. I asked Mazda dealer, they charge me again for investigation fee, but there was completed no result they can find. The service rep suggested me drive my car again until more problems show up or at the moment it dead.
I believe there is something seriously wrong with my car. I think it is urgent for me to get some help!!

Just a update. Now, the car is fine for 2 hours after I start driving everyday. After that, the light will come back sometimes. I noticed that, the rpm will goes up when the light on, and goes back when the light turns off.
I called my dealer again, they thought I need replace spark plug. By their point of view, spark plug is the only part related to the engine but not linked to the "check engine light".