The two main causes why your Hustler zero turn radius lawn mower may idle rough are the spark plug and air cleaner. If the spark plug has fouled or gone bad then it would need to be replaced. Sometimes just the spark plug gap is too wide and needs to be reset. Check your owner’s manual for specific information.
The other possible cause is a dirty air cleaner. If your Hustler mower has a foam air cleaner they can be washed out with soap and water, but if it has a paper air cleaner it would need to be replaced.
The model and serial numbers on your Hustler zero-turn mower can be found on the frame of the mower.
NOTE: if you need a part for the small engine in your Hustler zero-turn mower, there will be a separate model/serial number for the engine. Here are the small engines that are available in your Hustler mower. Visit the page of the engine you have to find out where the model/serial number is located for your small engine model: