Rough Idle when Engine is Warm

[cmcculley]

2011 Mercruiser 350 MAG MPI - 1A627350

When cold engine runs about 750 rpm, and gradually reduces as engine gets up to temperature.
When temp gets around 130F the engine idle reduces and the engine will stall.
Engine will start immediately back up and idle around 530-550 and is rough. Doesn't usually stall again when it is warm, but it stumbles often.
But will run 5000 rpm WOT with no hesitation
Replaced IAC with an automotive (Ford Windstar), this IAC has a spring. Now because of the spring when it starts it revs up until the IAC takes over reducing the RPM's. Runs a little better but mostly around 550rpm or less.
Fuel filters replaced
Fuel pressure is 40psi and holding

Only other thing to note is raw pump hose came loose this summer, and we tried to idle back to dock until the PCM shutdown the engine around 200F. I don't think it overheated, but there was steam where the boat was filling up with water in the bilge.

 

[alldodge]

this IAC has a spring

Guess I would ask that the previous IAC did not have a spring.

The Merc part number is 862998 which is also 1F2Z9F715AA used of Ford Windstar 2001-2003

 

[cmcculley]

That is correct

 

[alldodge]

Need some clarification to move forward.
Its my understanding the you had a ruff idle until replacing the IAC, now it does idle correctly and there was a bit of an overheat, but no issues from that have shown up.

If all is correct, what is the question being asked?

 

[cmcculley]

Sorry for the confusion. After replacing the iac it still dies after first startup from a cold engine and still runs rough at idle, but is slightly better with new iac.

Also before and after iac when in gear at idle runs a perfect 600 rpm +- 10.

 

[cmcculley]

I would also like to add the following I checked tonight.

Took out a few plugs. They look great with just a slight brownish tint

I will have a can bus diacom cable in a few days, what should I look for? Tps? Shift interrupter? Etc.

 

[tpenfield]

I would also like to add the following I checked tonight.

Took out a few plugs. They look great with just a slight brownish tint

I will have a can bus diacom cable in a few days, what should I look for? Tps? Shift interrupter? Etc.

Are you getting a code reader or the full Diacom software?

 

[alldodge]

Being a 2011 things have changed from the manual I have. There was a similar issue in another thread and Fun Times brought up some points about things changing and only being documented in Merc bulletins and such. With that, I would look at connections for corrosion including the MAP sensor. The PCM is trying to correct the issue but its not getting a signal correctly.

Check that the vacuum line going to/from the fuel pressure regulator to the intake and is not cracked. If you can Tee into the vacuum line and install a vacuum gauge, note if its steady or bouncing.

 

[cmcculley]

I have Diacom full software.

I have inspected the vacuum line, but I have not checked for proper vacuum. I did pull the regulator off the fuel pump to see if it was dirty. The screen was clean and looked new. I will check the vacuum with a guage. There doesn't appear to be a sensor for vacuum going to the PCM. The fact that I have 40psi constant on the fuel rail doesn't indicate that the pressure regulator is working?

 

[cmcculley]

I have purchased the PCM09 service manual, and also have the Selco manual for this engine. The Selco manual is lacking and doesn't really include this engine with the emissions sensors on it. I am hoping the PCM09 manual will include some troubleshooting tips. Is there another manual that I should have?

 

[alldodge]

I don't think its a fuel pump or regulator issue, mentioned the vacuum gauge on the regulator line because that is a place where a gauge can be connected. There is no other vacuum ports on the motor.