Ref to your Engine surging:
I have a vitz 08 and at very low speeds (around 20kmph), I feel that if i lift the acceleration pedal the car kind of tries to slow down itself (giving a slight jerk). To mantain a slow speed of 20-25, I have to keep the slight pedal pressed. My understanding is that it should keep the momentum on a flat track if i lift the pedal.
Also, the same behavior is experieced when I am at high speeds (60-70) and apply brakes sloftly to slow down, upon reaching 20-30, it gives that slight jerk again and slows down quickly...
Not sure if this is an intended feature?
Changed spark plugs recently, air filter is clean, throttle body is clean.