Mercury Optimax revving up high RPMs in neutral

Just recently I’ve had my Mercury optimax sitting in neutral only to have the RPMs increase. The only way for me to get it to go back down was to shut the motor off put it in neutral and start the motor back up again. Now today the RPM’s would not go back down at all. I would shut the motor down put it in neutral only to start the motor back up and it would take off at high RPMs still in neutral. Anybody have any similar issues like this and what was your fix?
Thanks !!

my first thoughts are if everything is mechanically sound,ie,throttle cable/linkages are not coming apart allowing excessive movement of the throttle plate,you may have a vacuum leak or low fuel pressure causing it to go lean and revving up.
I would find this out asap so you dont burn up the motor from being lean.

if it is new enough the throttle is electric,you may have a bad throttle position switch or a idle increase switch that is stuck in the increase position,or possibly a bad throttle body.

what ever it is it isnt safe until repaired as you know.

I had a similar problem of high rev at start up. It was a torn fuel regulator diaphram.

Same issue mine was Throttle Position sensor and the O2 sensor. Take it in and have it checked out and hope it is throwing a code at first mine never thru a code until it got bad enough.

Thanks guys !!
I’ll call for an appointment!!

Brought my Opti into the shop they hooked it up to the computer and it was the throttle positioning sensor she’s running like a dream now !!!

glad it’s running better…hopefully a permanent fix.

and, what year motor is it? some newer (~2015) Opti’s have compressor issues that result in the same kind of high-rpm revving when in netural. Merc redesigned the compressor in the middle of the run that year and ones with the old design need to be replaced – hopefully before causing other damage.