1998 Mercury 150 HP High RPM Idle !!

[Joseignacio]

My Mercury got stuck on a high RPM (3,500) after arriving at a destination and did not want to shift to neutral. When forced into neutral, the RPMs went high (3,500). The problem went away when I accelerated again and tried to shift to neutral. At that point it went back to around 900. It did it again when coming close to the pier to dock.

 

[crem1]

Re: 1998 Mercury 150 HP High RPM Idle !!

Could be in need of a major carb cleaning. Removal and soaking in a solvent for a day, then installing a new carb kit

 

[j_martin]

Re: 1998 Mercury 150 HP High RPM Idle !!

Could just be something tangling with the linkage, or the throttle cable is failing. There's a couple of springs in the throttle arm that could be broken or something. That's way too much power to be out of control. Get it fixed before you cream a dock, or worse yet run over somebody.

 

[Dukedog]

Re: 1998 Mercury 150 HP High RPM Idle !!

One place you might look. Check tha trigger harness right behind tha flywheel. It goes thru a little clippy thingy at tha flywheel cover mounting stud with a plastic spacer and wingnut. That harness has to move freely back and forth when tha trigger moves. Sometimes that can cause some sporadic grief like what you are describing...............D

 

[Joseignacio]

Re: 1998 Mercury 150 HP High RPM Idle !!

Thanks for the replies !!
I tried the cables and all carb levers and spring and they all work fine.
The only difference from before this stated is that I did a complete tune up including spark plugs, (2) thermostats, fuel filter, water separator fuel filter and lower unit gear oil.
I don't know if any of these would cause this issue.
The outboard RPMs are high as soon as you start the engine even without touching the throttle.

 

[Dukedog]

Re: 1998 Mercury 150 HP High RPM Idle !!

Thanks for the replies !!
I tried the cables and all carb levers and spring and they all work fine.
The only difference from before this stated is that I did a complete tune up including spark plugs, (2) thermostats, fuel filter, water separator fuel filter and lower unit gear oil.
I don't know if any of these would cause this issue.
The outboard RPMs are high as soon as you start the engine even without touching the throttle.

None of that should cause your problem. If you don't have a MERC manual ya need ta get one.
Could be some kinda air problem, maybe carbs, maybe justa gasket leak causing a lean condition (not good). Could be some kinda timing problem with tha trigger and/or trigger linkage. You need ta go thru tha whole nine yards of link n synk, timing process. There's a whole bunch a things ta check, thus tha need for a manual ta start with..................JMO

 

[crem1]

Re: 1998 Mercury 150 HP High RPM Idle !!

When is the last time that you actually took the carbs off the power head and soaked all the parts in a solvent? Gum formation can play funny tricks with your engine

 

[Joseignacio]

Re: 1998 Mercury 150 HP High RPM Idle !!

1 1/2 yr....

 

[Joseignacio]

Re: 1998 Mercury 150 HP High RPM Idle !!

How difficult is this task to complete. Is it a do-it-yourself or take to a shop fix ?

 

[Dukedog]

Re: 1998 Mercury 150 HP High RPM Idle !!

Depends on your general knowledge of what your lookin' for and how it works plus having a (Genuine Merc) manual that expains and identifies things.
Could be something real simple but trying ta identify something on a computer is not always tha easiest/best way.................JMO