F90TLR rough idle

[jackmanjls]

At idle speed the motor dies or runs extremely rough. I can restart but it runs rough. I have been noticing over the last month that it doesn't start as quickly as it did in the past. It may take 3-4 cranks when it used to take 1-2 cranks.

I shocked the fuel system by replacing the water filter and before installing filled with AimsOil gas additive concentrate. The local marine mechanic suggested this. I then ran at least for 30 min.

At WOT it runs w/o any issues or so it seems. The tach at 25mph may be slightly higher than norm but I can't say for sure.

This issue started 2 days ago when I got a crab trap caught in the prop. Is this coincidence or could that have caused the issue? Maybe jump timing?

I've checked water filter and first filter coming into the motor and both were fine.

The plugs are all the same, black dry (not wet) coloring similar to a rich gas mixture. When it runs at idle it sounds like the restrictive rpm (for low oil or hi temp) has kick in but runs at high rpm.

I did an ohms check on the spark plug wires and they are between 5-7Kohms.

Any suggestions?

[boscoe99]

Check the wiring to and the connector for the ISC valve. It is a known "hotspot" in your model.

[tmann45]

What is your idle rpm?

Could it be remnants of the crab trap caught in the prop/lower unit? Have you remove your prop since this happened?

[jackmanjls]

The service manual says the following. There's not reference

4. Stationary test: With the engine off, the ignition, fuel injection, electric fuel pump, and ISC valve are checked. These tests can be performed quickly.

5. Active test: With the engine running, each firing cylinder has dropped and the engine speed is checked for changes to determine whether the cylinder is malfunctioning and the ISC valve is checked as well. These tests can be performed quickly.


Where is the ISC valve located?

Do you know if I look on boats.net do they actually depicted it as ISC valve or some other reference?

[boscoe99]

Item 10

2006 and Later F90TLR Yamaha Outboard INTAKE 1 Diagram and Parts

[rodbolt17]

the ISC is the Idle Stabilizer Valve, the rest of the world calls it an IAC.
it controls the intake air at idle speeds.
its also that rattle you hear,or should, when you shut the motor off.
it requires a laptop to properly test.

that so called shock treat most likely loosened up enough debris to start clogging VST filters and injector filters.

first couple things to do is check the VST vent,vapor canister if equipped,and fuel rail pressure.

fuel system shock treats,other than making me a lot of coin, are teats on a boar hog.

no such thing as mokanik in da can.

[jackmanjls]

How would I test the valve to see if it's functioning properly?

I'm assuming there's a connection to the ECM. Would I do a continuity test from ECM to valve?

Is the "hotspot" a continuity issue that is caused by corrosion or something else?

[jackmanjls]

RB17

You say:
first couple things to do is check the VST vent,vapor canister if equipped,and fuel rail pressure.

I know where the VST is but not the vent.

The boats on the lift. To do this I may have to put on trailor and bring in garage, hassle but can do.

While on the lift...If I check the fuel rail pressure and clean the FI's would that be a good start? I don't want to get to deep b/c dropping stuff into the water is really bad.

[boscoe99]

The cowling snags on the wire harness and pulls the wires. The wires can break internally ahead of or at the connector.

Here is another F90 port with a similar problem. This guy found several compromised wires. He fixed them and his problem went away.

http://www.yamahaoutboardparts.com/f...m-th24966.html

Not saying wires are your specific problem but the check by you is free.

Let us know what you find out.

[boscoe99]

How would I test the valve to see if it's functioning properly?

I'm assuming there's a connection to the ECM. Would I do a continuity test from ECM to valve?

Is the "hotspot" a continuity issue that is caused by corrosion or something else?

It is a wiring issue. Wires get snagged on and pulled by the engine cover. Over time the wiring fails.

[jackmanjls]

B99...i read the link and it sounds like what i got. your "hotspot" comment sounds like this is what's happening.

from what i read is it correct to say that the wires that go from the ISC are terminated in a connector and on the other end are hard wired into the ECM?

to troubleshoot do you think this is something that i should put the boat on the trailor or (based on your experience) can it be done w/boat on lift?

[boscoe99]

B99...i read the link and it sounds like what i got. your "hotspot" comment sounds like this is what's happening.

from what i read is it correct to say that the wires that go from the ISC are terminated in a connector and on the other end are hard wired into the ECM? YES.

to troubleshoot do you think this is something that i should put the boat on the trailor or (based on your experience) can it be done w/boat on lift?

The inspection can be done on the boat with the boat on a lift, in the water, on a trailer, suspended from a helicopter, etc.

Just take the cover off. Closely visually inspect the wires at their entrance to the plastic connector. An electrical inspection can be done via a continuity test from the wire harness at the ECU end all the way to the sockets in the connector at the ISC valve end.

[boscoe99]

RB17

You say:
first couple things to do is check the VST vent,vapor canister if equipped,and fuel rail pressure.

I know where the VST is but not the vent.

The boats on the lift. To do this I may have to put on trailor and bring in garage, hassle but can do.

While on the lift...If I check the fuel rail pressure and clean the FI's would that be a good start? I don't want to get to deep b/c dropping stuff into the water is really bad.

Water is like a magnet to tools and parts.

Let's say a part drops and falls on the gunwale of a boat. There is theoretically a 50/50 chance that it will (1) bounce into the boat and (2) bounce into the water.

Reality shows it will head for the water 99% of the time.

[boscoe99]

the ISC is the Idle Stabilizer Valve, the rest of the world calls it an IAC.
it controls the intake air at idle speeds.
its also that rattle you hear,or should, when you shut the motor off.
it requires a laptop to properly test.

that so called shock treat most likely loosened up enough debris to start clogging VST filters and injector filters.

first couple things to do is check the VST vent,vapor canister if equipped,and fuel rail pressure.

fuel system shock treats,other than making me a lot of coin, are teats on a boar hog.

no such thing as mokanik in da can.

Yamaha, not being part of the rest of the world, calls it an Idle Speed Con*****er. And it is a valve.

Idle air control (IAC) valve would be the more correct term IMO. Since it is technically con*****ing the amount of air allowed in, in order to control the idle speed.

But then Yamaha calls a control box a "binnacle" and calls an anti-ventilation plate a "cavitation" plate. And battery cables are referred to as a "wire harness".

Ah, the joys of the English language.

[rodbolt17]

and sometimes, in the event of a fever, the overheat warning will sound.
sometimes the translation just did not work.
like I said, a quick test of the isc is to simply listen carefully at engine shutdown.
it rattles while resetting to 100% in anticipation of the next restart.

if its stuck closed its going to idle slow and hard to start,to much fuel.

if its stuck open its going to idle very fast ,to much air.

that's why 99% of ALL EFI engine of all brands start at very high idle and slow down.

the ECU isn't very bright, it makes assumptions.

when it gets a start signal it defaults fuel,defaults ign timing and assumes the Idle air control is set at the correct position for engine start.
from there it takes a bit for the ECU to react to all the running engine inputs and set the idle speed according to its internal mapping.

this works for ISC,IAC and single electronic throttle body EFI motors.