Just trying to figure out how the ISC assembly works for future reference. From my manual, I see it has a hose to the intake silencer, a hose to each throttle body, and a vacuum hose with filter to the intake manifold. I assume the valve itself opens and closes as needed and allows air flow from the intake manifold into the throttle bodies. I believe the hoses to the throttle bodies provide a vacuum to suck the air in as needed from the intake silencer connection with the valve electronically contolled to "throttle" the air flow. What does the vacuum line from the intake manifold do? Am I way off base here? Also, I have read some posts about cleaning carbon buildup from the ISC assembly to fix idle problems. Where does that carbon come from? Maybe the breather pipe hooked from the valve cover to the intake silencer? The more I understand the less silly questions I will pose later. Thanks in advance.
post the full model number and carefully rethink how and what the ISC does and why its there.your partially correct,however the isc doesnt rely on filtered air and the airflow past the throttle plates is a fixed,known amount. all the ISC does is allow more or less air to maintain a steady smooth idle.
but the airflow will depend on which 4 stroke EFI model yamaha we are dealing with and not all 4 stroke EFI yamahas use an ISC valve.
Trying to figure what role vacuum hose #7 plays. I believe ECU controls the ISC opening allowing air from hose #1 (attached to the intake silencer) to go to hoses #8 & #9 (hooked to the throttle bodies after the throttle valves). When the ECU open the ISC, the vacuum through hoses #8 & #9 pull air from hose #1 allowing the engine to idle. What role does the hose #7 play in the process? It is attached to the intake manifold and is listed as a vacuum hose. Where hose #7 attaches to ISC assimbly is a filter. Maybe if you could sketch out (in words) the air flow process during idle I could understand better. Thanks.
yes, just not tonight, head hurts.
but the throttle shutters are set with a manometer and from there the ISC take over.
initial setting for the shutters is mechanical.
stupid ECU reallly doesnt know where the sutters are until the initial adjustments are made and then the link and sync process begins.
set up correctly the ISC allows more or less air but has no idea if the throttle shutter opening setting was done correctly.
Thanks for the reply. Now, if someone could explain that explaination that would be great. No offense, I am sure it is my lack of knowledge that does not allow me to grasp it.
next week ill have a better explanation as ill have another power head replacement on another F115 due to or fine fuel.
but the ISC is also known as an IAC to the rest of the world. the japanese translator missed it.
google speed density EFI and you will get a lot of knowledge.
Thanks for the effort. I have a general idea what the IAC (ISC) does. Just wasn't sure exactly how the connections all fit together and interacted as Yamaha put it together, specifically that vacuum line (#7) from the intake manifold. If you get a chance for a different explaintaion I'd appreciate it. Thanks for all the great posts.
Read a little about speed density efi and now I believe I understand what roll the vacuum line plays. It appears as a sensor input at the ISC (IAC) to help the ecu decide on how much air to allow in at idle. Maybe ????
Yamaha 4stroke - idle speed control ????
Linear Mode
