Release gas pedal but delay on deceleration

Hello. I noticed on my E87 116i petrol engine when press the gas pedal to maintain current speed on road or even when I want to speed up, thus when release the overpressed pedal to eliminate excessive innertia so vehicle reaches the speed of engine smoothly it does not. In other words when I release the excessive pedal, the engine increases power for 1-2 seconds and then starts to be stable as the pedal position. Please help. It's manual 5 speed transmition.