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I have a 2004 190 Nantucket whaler with a 115 efi 4stroke mercury. It was running fine all season and then all of sudden now its idling high and when going from neutral to forward or reverse is making load noise and thrusting to hard in that gear . When idling in neutral its idling higher now then before, my question ? Is there an adjustment where the idle speed can be turned down some or slowed down like it was before? Any help would be greatly appreciated

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The engine you have is actually a Yamaha manufactured engine in Mercury cowlings, so either Yamaha or Mercury service people may be able to help you out.

I have some EFI 2 -stroke Mercs, and on those, the idle speed has to be set by timing, not an idle adjustment screw like the old carburator engines used, something I am not able to do. So you may have to have the engine serviced by people with the correct diagnostic equipment. It sounds llike you need a trained professional service person to take a look at it.

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I was hoping to avoid that but you might be right. Thanks

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A FI engine can react to problems and set the idle high, but your throttle cable could have a restriction and that is easy enough to check.

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Since this came on suddenly, I'd want to know what changed, rather than just adjusting the idle.

If you take off the motor cowling, I expect you'll see that the throttle arm (that the throttle cable connects to) is not returning all the way to the idle position when you move the remote throttle to neutral - usually there are some marks to show that position, but you may need a service manual to make sure. If it is getting hung up, then you need to figure out why - could be the cable itself, or something in the motor linkage has come loose or needs lubrication.

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It was working fine earlier same day and then while out it started to have a problem, the only thing and I really think this is unrelated , was that I was using the livewell for the first time in years and it worked and then the live well stopped working , it used to blow a breaker on the fuse and I would reset and then it would work live well that is but this time the live well stopped working and didn't blow a fuse at all I think it might be the live well switch and everything else was fine and the engine didn't stsrat having a problem until about an hour after that. Again I am sure that unrelated but that's truly the only thing different that happened

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The shifting issue is connected to the fast idle.

How many hours on the motor? If more than 100, did it have the maintenance interval work done? How long has it been?

After looking at the linkage....

When was the last time the thermostat was changed? If > 2yrs, change it.

All the fuel filters replaced?

When was the last time the Idle Air Control (IAC) valve was cleaned?

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"When was the last time the thermostat was changed? If > 2yrs, change it. NOT SURE

All the fuel filters replaced? Yes all fuel filters replaced changed fuel pump last year also

When was the last time the Idle Air Control (IAC) valve was cleaned?" Again not sure I have never done it, how hard is it to clean these ? This is a 2004 115hp mercury 4 stroke efi , Also how hard is it to replace thermostat?
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I recall that Yamaha sold 90/115 hp power heads to Mercury in the early 00's before their 4 stroke models came out. If yours is such, it is often referred to as a Mercaha.

The thermostat is straightforward if you are mechanically inclined.

Do you have a shop manual? While OEM manuals are best, an aftermarket will suffice.

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I don't have a shop manual I was thinking of looking one up at library , How tough is it to get to the IAC valve to clean it, it seems it would make sense to start there , or do you think the thermostat is a more likely solution?

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I had a similar issue with a 2003 F115 with a higher than normal idle and the thermostat was the issue. Prior owner never replaced in 3 yrs. I think it would be the place to start. It is remove and replace versus a remove and clean.

FWIW - I have done some research on the engine forums this morning to aide in my responses.

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Thank You , is it difficult to do ?

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It's been so long, I don't remember. If it was hard, I would have remembered.

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Great , Thanks again

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Do you know where the thermostat is located on a 2004 mercury 115 efi 4 stroke outboard? I looked online to try and find the manual or a photo to locate but no such luck

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John and I talked offline and a good source of parts information and diagrams is available from Mercury Marine at:

https://public-mercurymarine.sysonlin...langDB=eng

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Phil check your email I sent you this
Phil
Thank You very much for all your help, I was thinking about exactly what happened when I noticed the problem when I was out fishing last Saturday, and the very first thing I noticed was when I was going from forward to shift to neutral it shifted down quickly to reverse and then when I tried shifting back to neutral again it went to forward, it was hard to get it in neutral , not impossible but it seemed like the neutral area had shrunk, I remember doing that a couple times while fishing trying to shift to neutral from forward and having it go past and into reverse, that had never happened before , again it wasnt impossible to get into neutral and I was able to it just was harder to do, not physical harder . I hope this makes sense , also when it was in its slowest position in forward or reverse it was faster then it was before and again idled faster in neutral. I am not sure the thermostat would have caused this and I am curious what you thoughts were. Thanks John

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Based on that additional description it sure sounds like a problem inside the shifter itself, or possibly in the cable(s) or linkage on the motor end. I would NOT drive the boat in this condition - you could lose control and get hurt.

Tim