From your Description it Sounds like the Plate that is Attached to the Carburetor (that the Throttle cable Attaches to) Thru Shaft (holds and Moves the Throttle Valve) has Loosened and is Simply Turning on the Thru Shaft and Not Moving the Thru Shaft and Throttle Valve at All.
>>You can View a Breakdown/IPL of the Engine and Mower at this Site Addy, http://jdpc.deere.com/jdpc/servlet/com.deere.u90490.partscatalog.view.servlets.HomePageServlet_Alt
and Enter the Model Numbers 14SB and Click Find. Then Select your Model from the Search Results Area. Then Select the Sectional File. Then Select the Section of the Mower you Wish to View Online. *You can Drag the View Windows for Better Viewing.*
Please, Do Not Hesitate, If I Missed Something or you Hit a Snag or this Does Not Correct the Problem, I am Here if You Require More Assistance.
Hope this Helps. Let me Know What Happens, Please. May the All Mighty Bless You and Yours. Be Safe and Be Happy. Thanks.