2007 80hp four stroke idle issue

[DamoRoo78]

Wondering if anyone can help , I've been having idle issues with my engine it starts and runs fine most of the time but occasionally will stall out or idle high and make a wierd sucking noise and blow air from under the cavitation plate anode , I've changed the idle air controler assembly ran a 100km round trip ran fine took it out 4days later and back to still having same issue,, any help diagnosing this issue would be much appreciated...

[DamoRoo78]

Sorry I replaced control valve assy not idle control assy

[99yam40]

Sorry I replaced control valve assy not idle control assy

Not sure what you are calling a control valve assy
Or what you mean by" stall out or idle high and make a wierd sucking noise and blow air from under the cavitation plate anode"

A better explanation may get you some response from some knowledgeable people

Possible it may be a lean sneeze you are trying to explain?

[DamoRoo78]

Ok I've added some attachments ,model number and control valve assy which I've replaced.. This doesn't happen all the time which makes it hard but I've replaced the part mentioned plus spark plugs ,thermostat ,oil filter all fuel filters ,fresh oil and fuel ..tested fuel pump and compression tested everything is within spec.. When it happens its mainly slowing down from a run out to my fishing grounds as I come back off the throttle to go into neutral or just a slow ***** to sound the bottom for structure the engine will not idle and stalls .. When I try to start it it won't start unless I use the fast idle lever and give it a few big revs with that slowly back it off and hopefully it will idle .. Sometimes it does sometimes not..when it's running under fast idle lever there is a lot of air coming from under cavitation plate around the anode but not when it's running like normal, also a hissing air noise when under throttle that is not there when is running normal , when running properly it idles between 600 / 700 rpm. When it plays up it can sometimes idle at 400rpm and decrease slowly till it stalls or very rarely won't drop back to standard rpm of 700rpm and will idle high around 1200 / 1400rpm .. Hope that helps

[TownsendsFJR1300]

The hissing and high idle sounds like a vacuum leak.

When its hissing, pull the cowl off and listen real hard to find the spot. You likely have a broken vacuum line (split?) somewhere or a loose connection(vacuum).

That would also explain the occasional stalling, likely has a vacuum leak causing incorrect fuel air mixtures..

Good luck and please post your findings..

[rodbolt17]

at least now you have a spare ISC valve.

the only way you will find it is careful testing,preferably with the laptop , when its acting up.
remember ISC is NOT monitored for faults.
above about 2000 RPM the ISC is commanded to 100%.
if it sticks or fails to RECIEVE the electrical command to reset to about 60% at idle it will make a lot of hissing,the exhaust will bubble and it either idles very high OR stalls.
for those that don't believe simply start your speed density type EFI car.
unplug the vacuum line from the power brake booster at the intake manifold.
be aware that engine idle speed will jump up by about 1000 RPM.

what you will be looking for with the laptop,use the graphing feature, is TPS, ISC % command and map sensor feedback.

ALWAYS remember.
the ISC% value is a COMMAND from the ECU.
the ECU has NO clue if the command was actually executed by the mechanical part of the ISC.

if the ISC does not move mechanically from the 100% open position and the TPS value is normal you will notice a drop in intake manifold pressure.

occasionally for some odd reason, not all Yamaha ECU's read out MAP.
some read out inchs of mercury("Hg).

manifold absolute pressure is the INVERSE of intake manifold VACUM.

at or near WOT MAP will be close to barometric pressure.
however VACUM will be close to 0"Hg.
gets confusing but I don't program ECU's.

our example, baro pressure is 30"Hg today. weather is nice.
this is locked in at key on and remains 30"Hg for the rest of THAT key cycle.
a normal running 4 stroke will typically idle at 20-22"Hg intake vacuum.
that correlates to 10"-8"Hg manifold pressure.
as the throttle plate opens(or an air leak or a NON closing ISC valve) allows more air into the intake you will see intake vacuum FALL however the inverse is true as you will notice manifold absolute pressure creeps towards the barometric pressure.

over the years and models I have seen it displayed in PSI,"Hg and "Hg pressure.
gets a bit confusing until you get used to what its trying to tell you.

I can tell you the ECU mapping of a 2010 F250 will allow the engine to run at about 22,000 ft above se*****l.
however its up to you to find water thin enough to operate an outboard at that altitude.