1999 3.0 Mercruiser has a rough idle and diesels on shutdown.

[Nohfire53]

My 1999 Mercruiser, 135hp has a rough idle and diesels when I turn it off. Also, when the motor is warm, I still need to give it throttle to get it started. Any ideas? Should I have the carb rebuilt or is there a "quick fix'? Maybe and OEM carb the works better? Any help would be great.

 

[Bondo]

Re: 1999 3.0 Mercruiser has a rough idle and diesels on shutdown.

Should I have the carb rebuilt or is there a "quick fix'?

Ayuh,... I'd start with a full, 'n complete Tune Up, 'n Service....
If that don't Fix it, rebuild the carb...

 

[Jmunk]

Re: 1999 3.0 Mercruiser has a rough idle and diesels on shutdown.

Every 3.0 that I have ever been on will diesel on shutdown after a coming down from a hard run if I didn't let it idle for a min or two prior to shutting down. What is your idle speed at?

 

[Don S]

Re: 1999 3.0 Mercruiser has a rough idle and diesels on shutdown.

Below is a service bulletin from Mercruiser on the subject of runon and dieseling. In most cases, setting the idle rpm to specs (650-700 rpm) and allowing the the engine to idle for a minute or so after a run will cure the problem.