F90TLR Idles High!!!

[adbama1441]

I’ve had a brain teaser. I have a 2010 F90TLR with 116 hrs. When I start the engine it goes directly to 2800 rpms and holds there 5,10 minutes or longer. That’s currently btw. Let me now go to the beginning. Last spring I bought this boat from a friend. His father passed and he wanted to sell the boat. I know how the boat was maintained I had used it quite often. This problem happened overnight. The problem then was when engine started it would start and idle correctly but after a long ride when trying to idle down out of gear it would keep a high idle of around 1500 rpm. So I would kill the engine and then restart the engine and it would usually fix it temporarily and sometimes it would go straight back to high or higher idle. I put the boat in the shop and the technician had it for three months replacing the throttle body and tps sensor. I get the boat back and nothing has changed. I have changed the temp sensor and IAC valve per the ydis diagnosis. Now when I start the engine it goes to 2800 rpm and doesn’t change even when the engine is killed and restarted. And the ydis is now flagging the tps, intake temp sensor, intake air sensor, and intake air passage. Any help we be greatly appreciated. Thanks for reading my novel.

[fairdeal]

what are the values you see in YDS for intake air temp and pressure at key on -
is the temperature correct? does the pressure match atmospheric?

I'm curious - if you unplug the IAC
will the engine start? if so, what does it idle at?

[99yam40]

did you set things to spec when putting in the new ones?
have you measured the voltage from ECU to the sensors to make sure it is staying in spec
some thing may be dragging down the voltage

[adbama1441]

I installed the new parts yesterday evening and haven’t had the chance to run the YDS again. I will check the numbers again. But I have noticed something interesting when the engine is started and goes to 2800 rpm the IAC is still sucking air ( a noticeable hiss). That shouldn’t be happening but only at low idle???

[adbama1441]

[boscoe99]

Carefully inspect the wiring to the IAC valve. Motors in your timeframe were noted to become subjected to physical damage.

[adbama1441]

Where is or is there a procedure to set sensors to spec? Also when the engine is idling at 2800 rpms I can plug off the ISC Valve tube the idle comes down and the engine purrs like a kitten. ♂️

[99yam40]

service manual for your motor should have the procedures and specs.

maybe the motor is trying to move ISC, but it is not responding
Just because the ECU tells it to go to a certain % does not mean it goes there

[adbama1441]

Good advice! Thank you. I’m gonna dig into the ISC wire harness tomorrow it’s a four wire sensor so it’s got a ground, power, and two signal wires right. The only book I have for the engine is a seloc manual and the wire diagrams are non existent unless I contact them, and the description for testing the sensors are contact a certified Yamaha dealer. I will post on what I find.

[fairdeal]

gonna dig into the ISC wire harness tomorrow it’s a four wire sensor so its got a ground, power, and two signal wires right.

Its not a sensor, its a 'stepping motor'
with two coils



IIRC, all four leads go to pins on the ECM,
and one or the other at any time may be 'hot' or ground'
depending on the internal logic/action of the ECM

Consequently checking each for continuity is a PITA
of finding the appropriate pin at the ECM connector.

But as Boscoe pointed out above,
you may be able to see physical damage to the wires
where the cowling has pinched or crushed them.
Have you examined them carefully?

You have the YDS program?
what does the valve sound like when you do the "ISC Stationary test"

[fairdeal]

when you do the ISC test,
you should be able to see the valve actuator extend & retract.

(DO NOT remove the tamperproof Torx screws to get a better look at it)

[adbama1441]

I have inspected the wires at that point of connection, one of the wires on that harness looked kinked at the point of entry of the ISC connector. Since I couldn’t find any resistance values to test the ISC with a meter I had just assumed it is bad. If I unplug it the engine still cranks! No change in rpms. I do have yds. In the previous post I sent two screenshots of the outcome the baro was dead on for the day. I did notice that the isc on both yds reports @ 824 rpm isc is open 10% and @ 2800 rpm the isc open at 10% while the throttle valve opening was at 6.1 percent and didn’t move at whatever the engine was idling at per reports.
Please correct me if I’m wrong!! The isc acts as a con*****ed vacuum leak for low idle purposes. When the throttle is advanced the isc closes the con*****ed vacuum leak off right.

[fairdeal]

I The isc acts as a vacuum leak for low idle purposes. When the throttle is advanced the isc closes thevacuum leak off right.

Yes, the ISC valve is a way for the ECM to effectively 'open or close the throttle'
since it can't move the actual throttle plate itself.

(engine models with 'electronic throttle body' do not have an ISC valve - no need for it)

But as 99 Yam pointed out above,
there is no feedback to the ECM from the ISC;

the % value you see on YDS is only what the ECM 'wants' the ISC to be at -

- what it 'thinks it has set it at'.

if the ECM has sent the electrical impulses to close the valve -
but they never get to the valve because the wires are bad -
the ECM has no way of knowing.

[adbama1441]

One other “Q” when the isc test is accomplished is it a static test or does the engine need to be running?

[fairdeal]

there is a 'stationary test'
with the engine off, it fully cycles the ISC -
fully extended to back in - once.
You can hear it, and see it move.

then there are two active tests
one at idle, which opens the valve 100%
the other allows a specific setting (I have never used it)