Mercury Expert Needed

[Cub48]

Hi Guys Today I took my boat out 2016 175 Pro XS After a run of about 1 mile at 40 mph stopped to fish put in neutral my idle was about 1200 RPM hit the hot foot same thing 1200 RPM dropped in gear drops down to normal put back in neutral 1200 RPM shut engine off restart idles down like 600 to 800 RPM dropped in gear idles like normal put back in neutral idle down to normal. Left there ran up the river a little, Stopped and put in neutral 1200 RPM hit hot foot 1200 RPM shut engine off started right back up idled down to normal drove to ramp at about 1000 RPM let off normal, Has anyone had this problem. Could it be programing, sensor, or something else, Could fuel cause this ? I run 100%. New to Mercury and direct injection. No alarms. Also does anyone run premium plus mercury oil instead of the opti max oil. Was told by Mercury Tech it would be ok unless i idled around a lot then carbon would build up. Cub48