2000 250 OX66 Idle Problem

[jlopvar]

Twin engine set up...the other day at cold start up starboard engine goes to 1500+ rpms and never settles into normal idle rpm of around 700-800. At times it surged between 900rpms to 2000rpms but eventually settled to around 1000 rpms. After leaving dock boat ran fine in gear...but when in neutral problem returned, high rpms, and throttle became very sticky and at times down right hard to shift into gear.

Port engine ran fine.

Any thoughts? 02 sensor or thermostat?

What about the throttle issue?

Any help is very much appreciated. Thanks.

 

[rodbolt]

Re: 2000 250 OX66 Idle Problem

gear case for that engine retails for about 2800 dollars.
keep bang shifting and trying to snatch it out of gear and you will find out.
O2 sensor is NOT monitored by the ECU unless its unplugged then it fixs fuel rich at idle and lean above 4000 RPM. DO NOT run above 4000 RPM.
any other sensor the engine defaults to 7 degrees BTDC and idle speed is increased to about 1100 RPM.
motor is trying very hard to tell you its sick and please call 911 before I die.
and die it can.
you wilkl need either the diagniostic test lamp or a tune up spec guide and some test equipment to test all the sensors.
a stuck open t-stat or a defective temp sensor,not switch, can cause this as well.
but quit shifting until its fixed or you will compound the problem.