vitz does not accelerate well

[olcayto]

Hi everyone,
I am a new user, for car and for this forum..
I have a 2000 model automatic transmission vitz 1.0.
I have had this problem for 3 weeks.

First the car started changing transmission suddenly while accelerating from 60kms to 70s, it looked like it jumped transmission.

Then, some days later i saw the check engine light on.
Then took it to the mechanic. They changed sparkplugs, oil and air filters.

The light went away for a few days and it came back.

But by this time another problem developed. At traffic lights, I could not accelerate the car when I pressed the gas pedal. It looked it did not get any petrol inside, but then suddenly it accelerated and went on.

These days, anytime, I encounter gas pedal issue, the light comes on after some time or kilometers, being unable to accelerate may develop any time.

I asked some mechanic here, and one observed and said it could be a sensor around the engine that used to take the air inside along with the fuel. He suggested to change the spare part, but it is too expensive and i am not sure if the problem is that.

Can anyone diagnose or help anyway?
Thanks in advance.