Guyss..another help needed!!!

When I give full throttle and straight away release back to neutral position , the engine will scream BUT hang for like 2 seconds before it idles to neutral. Why it hang for 2 seconds and not straight away back to idle position?..Usually..once I release the throttle to neutral position..the engine will straight away back to neutral/idle position.

What should I do?..How do I troubleshoot this kind of problem?..Hope someone would help me out here...Thanks