Code 84 is the TORS - Throttle Override System. I got it on my Phazer when I installed an additional 2" riser and my throttle cables was stretched too tight. I had to re-route the cable under the handlebars to get additional length. It can also be triggered if you removed throttle cable from the throttle but did not install it correctly. There is a small metal clip that needs to be installed properly for TORS to work.
HAppened on my nytro on the bumping trail into the mountains a lock nut lossened off and then the bolt unscrewed a bit and caused the trottle to be slighlt opened when idleing it was around 2700 but once we screwed it back in and tightened the lock nut up the code went away you probably just have to rerout it so there is some slack in the cable good luck