Rpm drop fast after letting off throttle pedal

[toyotavios_11]

My car is 2007 model sedan with 1NZ-FE mated to U340 4AT.

Recently I notice that when the car is speeding up from 15km/h to 60km/h while the gear is at the point of time in 2nd or 3rd position, the moment I let off the throttle pedal, RPM needle will drop fast from 2000+ RPM to around 1000 RPM then surge a bit up to around 1200 RPM. I can hear there is a minor shock noise from the front and feeling a little bit of jerk.

While the gear is in 4th gear, either lock up or not, letting off the throttle pedal, RPM will just reduce slowly which I feel this is normal.

What are the possibilities of the problem?

[seatech30]

Is it possible the car is shifting into the next gear right around that point? What happens if you let off the gas at say 70km/h or 50km/h vs the 60km/h?

How's your trans fluid level?

[toyotavios_11]

Is it possible the car is shifting into the next gear right around that point? What happens if you let off the gas at say 70km/h or 50km/h vs the 60km/h?

How's your trans fluid level?

have no idea. perhaps i should perform fluid change.

[johnwk]

There's a transmission fluid dipstick. Just check it while the engine is warm and idling, and take note of the color on a paper towel.

[toyotavios_11]

fluild level is at correct level.
btw, i have solved the problem by cleaning MAF sensor.