Most of the time it is caused by low coolant. The idle air control motor has a wax element that is heated by the coolant.
Another possible cause is a vacuum leak. Hondas have a deceleration fuel cut off. This is how it works...
When the rpm's are above 1500 with the throttle plate closed it kills the fuel injectors to conserve fuel. This is why it surges. Engine rpm's go up, throttle plate is closed, kills injectors, rpm's drop, and fuel returns. Repeat.
Hope this helps.
Kevin