Intake Control Diaphragm
WARNING: This page is about a different car, the 1996 Honda Prelude. However, it is still accessible from the selected car via links, so may be relevant.
Connect vacuum pump to vacuum hose on intake control diaphragm. Apply vacuum. If diaphragm holds vacuum, intake diaphragm is okay. If vacuum does not hold, inspect vacuum line for improper connection and disconnected hose. If hose is okay, replace intake control diaphragm.