F115TXRB high idle speed

[Sparkieboat]

ok thanks ..I may keep it then...so if I put post #3 from this page where you said the F115 had more ECU failures than all other Yammys combined and the fact that you have only seen 6 in over 10 years..then Yamaha ECU failures are VERY rare indeed. I will clan my ISC today also, make sure there are no restrictions. you have been very informative..How is the fishing up there this time of year??

[99yam40]

So, Rodbolt is the cleaning of the ISC on the Yamaha recommended maintenance schedule charts or is it just something that just needs to be done and only a few people know of the need?

[rodbolt17]

nope, GM,Ford and Chysler dont reccomend it either.
however 30+ years of doing this type work has lead me to believe.
this speed density EFI setup has been around many many years in bothe single throttle and multi throttle configurations in both 2 and 4 stroke versions.
all work basically the same dont care where on this planet it was made.
luckily the laws of physics takes over and kinda dictates how to burn a fuel within a VERY limited range and make it work.
gasoline burns at about 14.7 parts air to 1 part fuel.
yes virginia it IS that simple.
at parts above about 15.5 parts air to 1 part gasoline it becomes to lean to burn properly and gets to hot.
at about 13.5 parts of air to gasoline the fuel mix becomes to rich to burn.
early gasoline engines actaully used gravity to dribble fuel through a needle onto a heated plate in the intake track.
very ineffcient very problematic but it worked.
carburators are a comprimise at ALL RPM ranges as it relies on intake and atmospheric pressures to move fuel.
EFI does not rely on intake vacum to move fuel.
the pump and injectors wil spray about any liquid regaurdless.
yamaha combustion chamber cleaner works very well and unless your getting a lot of carbon build up once a year is typically sufficient.
contaminated fuel,Ethanol fuel, incorrect proppng and internal mechanical issues can lead t excessive carbon in the intake.

[martinbryner]

Hi Rodbolt, thank you for all your helpfull info.
I will probably stick with it the way it is as this is my cheapest cost option.
Do you think that Mitsubishi may be using same ISC on cars?

[rodbolt17]

beats me, however there are only so may ways to make it function and all involve stepper motors.
some are 4 wire motors some are 6 wire. 6 wire just reacts faster.
newer EFI engines that incorperate electronic throttle valves did away with the ISC and use the throttle shutter to control intake air.
thats why the V8 and 4.2L v6 yamaha engines and the volvo ETC engines are so violent at start up.