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2010 Merc 30hp EFI 4S occasional stall when returning to neutral or low rpms

steveg_nh

Regular Contributor
I'm really starting to pull my hair out trying to figure out why my 2010 30hp EFI keeps stalling when returning to idle. Not always, more often than not it is ok, but it stalls enough that running in a river with strong tidal currents, I'm losing faith in the motor and letting my kids use the RIB it's on.


Last season, right after I bought the boat/motor used, I definitely had fuel issues, as the fuel system was dirty. I added a Racor fuel/water filter, changed the low and high pressure fuel filters, cleaned the VST tank and screen, and had the injectors tested and cleaned and screens replaced. I also tested fuel pressure on the rail and it was perfect. New plugs too of course, and new impeller. Went through the whole thing. It performed MUCH better, but the season was over, so I thought I solved all the issues.


So far this season, it still has the occasional stall when returning to idle quickly, or going to neutral. I changed out all the garbage gray fuel lines to low permeation rubber fuel lines, and have fresh fuel. The only thing I can think of is maybe the Idle Air Control valve is sticking, so sometimes it's ok and sometimes not? I looked at that last season and it appeared to working just fine, as I could hear it pumping and operating so I didn’t change it. Or is there a interrupter switch that could be failing? Someone recommended my throttle body may need to be adjusted but the service manual says it’s not adjustable.


When you bring it back to idle, it may drop to 600-700 and then catch and not stall, or sometimes it will hunt a bit and catch or sometimes it will just die. Hard to catch a video, because most times it's fine. Seems like the faster you return to idle speed, the more likely it is to occur.


Any thoughts or guidance would really be appreciated. I thought going to an EFI would solve a lot of the pain the neck issues I had with my old 2 stroke, but so far this hasn't been the case. Thanks a bunch.
 
IAC could be sticky or dirty. Remove and spray it down with TBC (throttle body cleaner) paying attention to plugger and pintle tip. Shake it dry and reinstall and run it several times.
 
Thank you. Plugger and pintle tip? Not sure what that is. Not the easiest to get at on this motor, but should be able to.
 
Still dealing with this. It's far and few when it stalls, but it did it today at of course, the worst time when the river current was ripping. If the motor is hooked up to a diagnostic computer, will it provide details on the performance of the IAC valve?
 
Still trying to sort out this motor. Frustrating. I out a new IAC in it yesterday (much harder to do given the access requirements), and it still is doing it. Actually had a bit more of a rough idle than I recall at times, with a flutter and drop in RPMs before it would stall. And it stalled like it does once and while, going back to neutral. I raised the white flag and called a local mercury shop, and she told me the if it's not throwing a code (alarm) the ECU won't tell them anything, so they will be hunting. Is that true? It wouldn't report a stall issue? She made it sound like they wouldn't have much luck unless it was readily reproducible, and diagnostic software won't help me.

I like fixing my own stuff so I learn, and because over the years I've started to lose faith in repair shops doing things right, but I feel like this is over my head. I've had folks recommend throttle body issues (possibly), but I hate to keep swapping parts without confirming symptoms and results of them.

I was thinking maybe a bad neutral safety switch, but that wouldn't explain just a low RPM stall.

I would really be grateful for anyone that may have some input.

Thanks.
 
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