2010 90HP EFI 4-stroke Merc dies after throttle and runs rough after warm

[jeepdude2]

I have a 2010 90 HP EFI 4-stroke mercury.

I bought the boat from my father in-law who said it did not have any issues. Obviously it does.

So when i bought it there was an issue with fuel starvation due to the fuel pump cavity not being drained for winter storage last year.
I replaced the internal float and no more starvation. I also replaced the IAC at the same time, to be safe.

So my new problems are these and I am hoping someone can point me in the correct direction, so i am not aimlessly throwing parts at this thing.

When I go out to the boat and it is cold, it will start up and idle normally and use low throttle normally.

Once warm I have two issues:
1. it idles roughish. it isn't loud or starving for air or fuel, but the rpms fluctuate 100-200 over and over again. this fluctuation in RPMS will last until you get over 1/4 throttle.
2. If i am running the engine at any descent rpm 2500 or above, and i pull the throttle back quickly to idle she just dies. She will start back up with no issue right after though.

These issues lead me to believe it is a sensor. MAP, or TPS were my guess's but I am hoping for some knowledge so I do not have to keep guessing.

Thank you in advance for your help,
Nick

 

[alldodge]

I would check fuel pressure

 

[jeepdude2]

Looking for more help.
I have checked the fuel pressure and it is stable staying right around 45 PSI
I have also changed the MAP sensor just to see if that was the issue.

Would everyone's next guess be the TPS(throttle positioning sensor)

I am out of ideas.
there are no beeps coming from the helm, and it runs fine at full throttle.

 

[ondarvr]

Have you plugged it in to read any codes?

 

[alldodge]

Not an OB guy but your issues sound like the IAC, and I see you have replaced it. Either that or a vacuum leak. Is there a place to attach a vacuum gauge?

 

[jeepdude2]

There is no way to pull codes without pulling the boat as there is no marina on my lake. I also do not own a trailer.
I will see if there is a spot to put a vacuum gauge as i did not consider a secondary leak.

 

[Rip & Tear]

There is no way to pull codes without pulling the boat as there is no marina on my lake. I also do not own a trailer.
I will see if there is a spot to put a vacuum gauge as i did not consider a secondary leak.

What ended up being the problem? I'm having similar issues

 

[tpenfield]

Sorry to say, but jeepdude has not been on the forums since 2017, so doubtful we will get an answer.

Closed.