# Yamaha F70 Intermittent High Idle



## Docndan1 (Dec 16, 2019)

Was fishing a new area out of state recently and nailed a couple of firm sandbars at 25-30mph inside the "channel". Everything seemed fine after that but noticed that sometimes now it'll rev up to 12-1400 rpm when shifted into neutral.

It's perfectly normal 80% of the time, and it happens seemingly more at the end of the day and never at the beginning. 

Could I have knocked something loose in the impact? Any ideas before I take it to the shop? Thanks


----------



## Lowtidelowlife (Aug 19, 2014)

Pro xs will kick up idle in neutral if it senses battery needs a higher output charge. Does Yamaha do the same thing?


----------



## Docndan1 (Dec 16, 2019)

I haven't noticed that before on mine, and I ran the old battery down when I first got the boat. I hooked it up when I got home and it was good on battery. Thanks for the suggestion though


----------



## Frank Ucci (Jan 20, 2019)

Throttle/shift linkage? Maybe it got knocked a bit off on the grounding.


----------



## Docndan1 (Dec 16, 2019)

I'll definitely check that out, thanks


----------



## Docndan1 (Dec 16, 2019)

Still having trouble with this. The throttle is definitely a little sticky but what confuses me is that if I turn it off for 10-20 seconds and turn it back on, it idles normally at 700 rpm. If it runs in gear for a couple more minutes, it returns to the high idle problem.
The other day after running for an hour, I shifted into neutral and it jumped up to 2000 rpm. Turned ignition off and motor continued to run, got worried about it and pulled the kill switch. Still ran for 30ish seconds before shutting down. Turned back on a min later and idled normal at 700 rpm.
Anybody??


----------



## Frank Ucci (Jan 20, 2019)

On the top left side of the motor there is something called a thermo-sensor, located near the thermostat housing. It has a plug on it which ties it into the engine wiring harness. Check that the plug is free from corrosion and fully engaged. I don't know much about the logic of these engines, but if that thermo-sensor is sending a false signal to the ECU, perhaps the ECU thinks the engine is cold and is raising the idle until it thinks the engine has warmed up sufficiently. If the plug is corroded or if the thermo-sensor is failing, it might account for the intermittent problem that you're having. If it were me, I'd take the boat into my nearest Yamaha dealer and pay an expert tell me what was wrong with it.


----------



## Fish’n guy (Apr 19, 2021)

Docndan1 said:


> Still having trouble with this. The throttle is definitely a little sticky but what confuses me is that if I turn it off for 10-20 seconds and turn it back on, it idles normally at 700 rpm. If it runs in gear for a couple more minutes, it returns to the high idle problem.
> The other day after running for an hour, I shifted into neutral and it jumped up to 2000 rpm. Turned ignition off and motor continued to run, got worried about it and pulled the kill switch. Still ran for 30ish seconds before shutting down. Turned back on a min later and idled normal at 700 rpm.
> Anybody??


Having same issue did changing the sensor fix?


----------



## Docndan1 (Dec 16, 2019)

Sorry for the delay, I never did change the sensor, it seemed to be an air leak and replacing stuff fixed it


----------



## Fish’n guy (Apr 19, 2021)

Thanks , I’ll have to dive into it more to see if there is a air leak happening


----------



## Fish’n guy (Apr 19, 2021)

could not find any air leaking by, just to give a run down on engine for info, 2014 70hp Yamaha 4 stroke 738hrs, new thermostat. Thermostat was checked it’s fine. Problem, after running at @ cruising rpm 43-4500rpm for 10mins, moving the throttle back to idle/neutral the rpms pick up to 2000-2400rpm, shutting the engine off and restarting the engine returns to 700rpm.
The engine started doing this a about 1yr ago but would only go to 1400rpm in neutral but return to 700rpm after about a min and only happened a few time last season. This season it has done it everytime after cruising. I want to think something is not closing are the away with the engine in neutral. 
new throttle/ cables last yr professionally installed no issues. 
Any suggestions would be great. Likely going to try to get in to a shop for a professional to look at sooner than later.
Thanks


----------



## Sejoe777 (Aug 23, 2021)

I would check the idle air valve… clean it and see if it fixes the problem its toward the front of the motor behind where the control connection goes pull the plastic back and you will see it.. you need some torx buts with the hole in the center


----------



## matthew9778 (2 mo ago)

Did


Fish’n guy said:


> could not find any air leaking by, just to give a run down on engine for info, 2014 70hp Yamaha 4 stroke 738hrs, new thermostat. Thermostat was checked it’s fine. Problem, after running at @ cruising rpm 43-4500rpm for 10mins, moving the throttle back to idle/neutral the rpms pick up to 2000-2400rpm, shutting the engine off and restarting the engine returns to 700rpm. The engine started doing this a about 1yr ago but would only go to 1400rpm in neutral but return to 700rpm after about a min and only happened a few time last season. This season it has done it everytime after cruising. I want to think something is not closing are the away with the engine in neutral. new throttle/ cables last yr professionally installed no issues. Any suggestions would be great. Likely going to try to get in to a shop for a professional to look at sooner than later. Thanks


 Did you ever figure out the problem? I have a 2014 f70 with 812 hrs doing the same thing.


----------



## matthew9778 (2 mo ago)

Docndan1 said:


> Still having trouble with this. The throttle is definitely a little sticky but what confuses me is that if I turn it off for 10-20 seconds and turn it back on, it idles normally at 700 rpm. If it runs in gear for a couple more minutes, it returns to the high idle problem.
> The other day after running for an hour, I shifted into neutral and it jumped up to 2000 rpm. Turned ignition off and motor continued to run, got worried about it and pulled the kill switch. Still ran for 30ish seconds before shutting down. Turned back on a min later and idled normal at 700 rpm.
> Anybody??


Did you ever find out the problem? I have a 2014 f70 with 812 hrs acting the same way.


----------

