Welcome. Thank you for choosing Just Answer.
your speedo has nothing to do with your idle, unless your bike has an electrical problem that is affecting both.
your speedo is a stand alone system. it is not affected by nor does it have anything to do with your fuel management system.
you can remove the speedo and have it checked on the bench tester at the dealership.
you can disconnect the speedo and see if it affects your idle.
you should also check the system voltage by measuring the battery voltage with a hand held volt meter with the engine at about 2,000 rpm. it should be between 13.5 and 14.5 vdc. let me know if it is not.
voltage problems can also occur if your ignition switch is not tightly mated to the harness connector. you should lift the dash and verify the connector is tight and that all the pin connections are clean and not damaged.
it's also possible your speed sensor has failed, but again....this would not affect your idle.
your symptoms point to an electrical problem, possibly associated with the speedo, or due to a system voltage problem affecting your speedo and ignition.
let me know if you need more help.