Engine Idle issue -- need help

[SeaRenity]

I have been having this issue for almost a year and would appreciate any feedback from the engine PROS! My starboard engine starts fine than after a minute or so the idle drops, engine pings and I smell and see a sheen of gas from exhaust. If I raise throttle it runs fine, it will stay this way till it reaches operating temp somewhere around 160 degrees than it idles and runs perfect.
I have changed distributor, rotor, injectors, CF3 module, fuel filters, plugs and wires. I also replaced ECT sensor. Does anyone have any ideas? Thanks

 

[Espos4]

2 thing i would do next are a compression test and also have a tech check for any fault codes.

You may have a cylinder not sealing properly or even a bad spark plug.

How many hours on the motor?

 

[SeaRenity]

850 hrs, no fault codes. but why would it run great after warm up if it was a cylinder or spark plug issue???

 

[Wanderer 290]

I would check the the engine temp sensor. If it is faulty the engine parameters such as fuel air ratio and iac will be off also. Try swapping sensors between engines and see if the problem follows?

 

[scoflaw]

The IAC moves when cold, and failure prone with that ecm

 

[JimT]

Swap the IACs and see if that corrects the problems. If the IACs have never been replaced they are overdue to fail.

 

[Espos4]

850 hrs, no fault codes. but why would it run great after warm up if it was a cylinder or spark plug issue???

There’s a lot of magic that goes on inside the engine. I can’t answer your question, but having the compression test results and any fault info from the ecm can rule out or confirm certain things, and possibly point you in the right direction.

 

[Andy Izzard]

Hi SeaRenity

Not sure if this will work for you but here goes. My starboard 350 mag mpi (2000 310 sundancer) had the same issue. Cold start all good then when warm with the lever at idle it would not idle. But stay around 1200 to 2000 rpm. I found a poor connection in the TP (throttle position) sensor. 3 pin plug near the inlet butterfly. Try and clean the pins both male and female. On the female side try and bend them ever so slightly to make a good connection. Refit and try. Good luck.

 

[d-reed]

If this thing is fuel injected there will be 2 coolant temp sensors, one for the guage and one for the PCM to control fuel trims. Make sure you check both of them. I'm not a boat Technician but an Automobile Tech, but I think I am correct about there being 2 sensors.

 

[Wanderer 290]

I believe your are correct about 2 separate temp sensors. 1 is a sending unit and one is a sensor. If the sensor is not functioning correctly, ie indicating a warm temp when the engine is cold, engine parameters and performance will not be to specification.

 

[Jeff Delbuono]

Had same issue with my 5.0 efi. Was the engine control sensor located at the t stat housing. This tells the computer to run rich at cold and thin out when warm. Had smell of gas, little smoke at start and sheen on water. Changed it out and fixed the problem