2008 115hp Etec head scratcher

[Ring King]

What would cause my engine to randomly run a couple hundred RPM too high when at idle? Not like running so high that it slams into gear but high enough that its noticeable to the ear. It might run fine for half a day and then when idling in neutral looking at the graph or something the RPMs will go up for no reason. You can get on plane and run for a bit and then stop and the problem will go away. Have occasionally had the RPMs skyrocket almost to red line when in neutral as well. Can turn the key off and crank it again and it might be fine or it might run away again. Usually this is a progression in symptoms culminating in a situation where you crank the engine and then when you shift into forward or reverse you can't get the motor to do anything above idle. You can advance the throttle lever and the RPMs stay the same but the motor will make a droning noise as if the butterflies are opening but there's no increase in fuel/air mixture to cause the increase in RPM.

The first mechanic that looked at it when it left me on the lake said the TPS was found to be out of range and sticking. They adjusted it back into range but noted that it could be a problem again in the future. Or that's what was written on the work order. I got about 7 trips out of it before the symptoms started coming back and eventually left me stranded again. The second mechanic said that while running in the test tank and "droning" he removed the airbox from the front of the engine and the incorrect voltage output of the TPS corrected itself and started running fine. I had him replace the TPS anyway. He didn't think the TPS was bad but suspected that maybe the rubber gaskets from the airbox had deteriorated over time and were allowing physical contact with the TPS and causing the strange issue so I had him replace those rubber gaskets as well. Again, I got around 8 trips out of it before the symptoms started coming back. Both of these mechanics were at different Evinrude certified repair centers. Neither of them have been able to figure out the issue.

Yesterday I fished a tournament out of the boat and it fired up fine when we launched. We idled out to where blast off was and shut the engine down. When our number was called to take off, I cranked up the boat, put it in gear, and it just started making the droning noise when the throttle lever was moved beyond just idling. We fished for a bit on just the trolling motor and then decided to idle to a rockpile about a mile away. After about 20min of idling the motor "fixed" itself somehow and we were able to get on plane and it ran great to our first spot. It again ran great when we went to our second spot. The next time I cranked the motor it wouldn't run at anything other than idle again and was making the droning noise. We gave up and tried to idle to the closest ramp. Again, after about 25min of idling it suddenly worked fine and we were able to run back to the launch and put the boat on the trailer. When it runs, it runs great and purrs like a kitten. No surging or anything. It's only when at idle in neutral that the RPM issues happen and even then when you put it into gear it runs great at idle until you try to advance the throttle past the "clutched in" position. The throttle linkage is working fine, and there's an airgap between the roller and the throttle assembly under the cowling when in Neutral position with the throttle lever.

The motor needs to go back to a shop but when we put it on the trailer yesterday after all the issues it was running fine so there's really nothing for a mechanic to diagnose currently.

I'm about ready to pull my hair out over this thing. I keep paying hourly labor fees to mechanics for their work but they aren't fixing the problem and I'm losing money in tournament entry fees as this was the second tournament that I basically didn't get to fish because of the motor problems.

Edited to add: Forgot to mention that the first time it did this I also had an issue with the stator and charging circuit that included part of the EMM. The EMM and stator were replaced and the symptoms are still happening with a brand new EMM. Afterwards I had a bad injector that was replaced and the rest were checked and found to be good.

[Bighare2]

Recommend this problem gets seen by the at the EOG. Post your problem also at https://www.etecownersgroup.com
there are several dealer techs that frequent the site. Be sure to provide the engine model number. E115xxxx
what has been checked for a restricted filter inside the vapor separator fuel return line?

[Ring King]

Thanks. I’ll post it there as well. I’ll have to get the exact engine model number.

The VST filter and fuel filter were replaced after the first time the issue happened and there was no change. When the injector failed last year I also pulled the fuel tank, drained completely, drained all fuel lines and went with new gas. The boat had sat for a year waiting on the new EMM from BRP so I did this as a precaution. The problems before the fuel flush remained even with new filters and new fuel.