RPM surging up and down when softly pressing the gas pedal

Hey,
i have a vw golf mk4 2000 2.0L 4cyl.
when I press softly on the gas the rpm start going up and down put when I press harder the rpm goes up normally without going down.
so while driving in traffic I press softly the gas pedal the car goes forward than stops than forward then stops. I thought it was an electrical problem but I was told it wasn't. Any idea what's the problem?

thank you in advance.