air control valve

[chenault]

What is the function of the control valve that admits air into the intake manifold on my 2005 F90TLRD?

[boscoe99]

It provides air so that the motor can run at an idle RPM. At idle the throttle valve(s) are fully closed. Air is allowed thru the IAC valve to give the motor the air that it needs.

[chenault]

So the IAC valve is normally open (de-energized) at idle speed to admit combustion air and closed (energized) when the throttle valve opens. Is that correct?

[boscoe99]

So the IAC valve is normally open (de-energized) at idle speed to admit combustion air and closed (energized) when the throttle valve opens. Is that correct?

I would not use the word "de-energized" at idle. The ECU is adjusting the valve at idle if and when necessary to control the flow of air. It is not an all open or all closed valve. A stepper motor opens and closes the valve in increments.

[fairdeal]

I would not use the word "de-energized" at idle. The ECU is adjusting the valve at idle if and when necessary to control the flow of air. It is not an all open or all closed valve.

As Boscoe explains, the Yamaha IAC is constantly working at idle,
as the ECU 'hunts' to maintain a constant speed.

A stepper motor has at least two windings; the IAC used on the early F225 has four.

This video shows an F225 idling,
the LED lights show the ECU constantly energizing 2 windings at idle
- although frequently 'toggling' which 2 of the 4.
The video ends with the engine being shut off - and the ECU 'resets' the IAC

https://vimeo.com/331842988

[boscoe99]

Fairdeal, have you any idea of the current that is flowing through the IAC valve to the ECU?

Reason why I ask is because a failing IAC valve has been known to take out the ECU. Excess current I would suspect. But...

Anyhoo, was thinking of a driver (relay) to activate the valve with the ECU con*****ing the driver. So that the ECU sees less current than it otherwise would. Sometimes I just think too much.

[fairdeal]

Fairdeal, have you any idea of the current that is flowing through the IAC valve to the ECU?

From resistance/continuity testing, and my LED experiment,
it appears that there are four actuating coils -

all with the same resistance from power to ground ~30 ohms

(parenthetically, there are two power feeds, so 2 coils share one power feed -
therefore one can measure ~60 ohms between the ground ends of each coil 'pair')

Unremarkably, grounding any one of the four coils results in a measured current flow of just under 400 milliamp

Yes, the "bad IAC kills ECM" story is a familiar one - but I don't know what to make of it.

From what I have seen with my F225, two of the four coils are constantly energized whenever the key is "on".
That continuous flow of 0.4 x 2 amps into the ECM clearly doesn't hurt it.
So what does?

[rejesterd]

Yeah, the schematic in my F50 service manual shows the 4 coils. It would be a pretty terrible design if any failed component like the ISC could take out the ECM like that. A fuse should blow before that happens. However, I do know that my ECM and ISC are grouped on the same 20A fuse.. I don't know if that's true for larger/newer models.

[rodbolt17]

and here again the amount of mis-infor,mation and misunderstanding is , well incredible.
the system at idle should maintain a constant REQUEST from the ecu.
the actual idle speed will vary about 50 RPM's as it overshoots and then under shoots using the timing and injector on time.
the ECU DOES NOT and CANNOT track the mechanical pintle..
any time the key is on the ISC has 12v+ supply.
the ECU controls the ground path.
at idle ;depending on the motor; you will see a REQUEST of between 35% and 60%.
at idle the ecu is looking at TPS,MAP and engine RPM.
if those inputs request an idle speed the ECU will toggle the ground path for the appropriate stepper windings.
so that dumb ECU, gotta remember it is a simple truth table device,if it cannot stabilize the idle speed that is requested via the MAP,TPS and pulser coil inputs, it simply starts toggling the ISC ground path.
that is when the ECU,ISC overheats occur.
that circuit was not ment to be continuous duty.
it is a request at idle,somewhere above about 1200 RPM,depending on the model, it opens it to 100%.
it acts as a dashpot.
the ISC is NOT monitored by the ECU.
no alarms nor codes for the ISC.
but if it gets toggled to many times by the ECU trying to stabilize the idle the ECU can overheat and die, sometimes taking out other componets while dying.
that rattle you hear at key off is the ISC resetting to 100% in anticipation of the next restart.

[pstephens46]

and here again the amount of mis-infor,mation and misunderstanding is , well incredible.
the system at idle should maintain a constant REQUEST from the ecu.
the actual idle speed will vary about 50 RPM's as it overshoots and then under shoots using the timing and injector on time.
the ECU DOES NOT and CANNOT track the mechanical pintle..
any time the key is on the ISC has 12v+ supply.
the ECU controls the ground path.
at idle ;depending on the motor; you will see a REQUEST of between 35% and 60%.
at idle the ecu is looking at TPS,MAP and engine RPM.
if those inputs request an idle speed the ECU will toggle the ground path for the appropriate stepper windings.
so that dumb ECU, gotta remember it is a simple truth table device,if it cannot stabilize the idle speed that is requested via the MAP,TPS and pulser coil inputs, it simply starts toggling the ISC ground path.
that is when the ECU,ISC overheats occur.
that circuit was not ment to be continuous duty.
it is a request at idle,somewhere above about 1200 RPM,depending on the model, it opens it to 100%.
it acts as a dashpot.
the ISC is NOT monitored by the ECU.
no alarms nor codes for the ISC.
but if it gets toggled to many times by the ECU trying to stabilize the idle the ECU can overheat and die, sometimes taking out other componets while dying.
that rattle you hear at key off is the ISC resetting to 100% in anticipation of the next restart.

Instead of writing a book on this boring ass topic, how about taking another look at the 200 HPDI issue that Cregis has....

[rejesterd]

and here again the amount of mis-infor,mation and misunderstanding is , well incredible.
the system at idle should maintain a constant REQUEST from the ecu.
the actual idle speed will vary about 50 RPM's as it overshoots and then under shoots using the timing and injector on time.
the ECU DOES NOT and CANNOT track the mechanical pintle..
any time the key is on the ISC has 12v+ supply.
the ECU controls the ground path.
at idle ;depending on the motor; you will see a REQUEST of between 35% and 60%.
at idle the ecu is looking at TPS,MAP and engine RPM.
if those inputs request an idle speed the ECU will toggle the ground path for the appropriate stepper windings.
so that dumb ECU, gotta remember it is a simple truth table device,if it cannot stabilize the idle speed that is requested via the MAP,TPS and pulser coil inputs, it simply starts toggling the ISC ground path.
that is when the ECU,ISC overheats occur.
that circuit was not ment to be continuous duty.
it is a request at idle,somewhere above about 1200 RPM,depending on the model, it opens it to 100%.
it acts as a dashpot.
the ISC is NOT monitored by the ECU.
no alarms nor codes for the ISC.
but if it gets toggled to many times by the ECU trying to stabilize the idle the ECU can overheat and die, sometimes taking out other componets while dying.
that rattle you hear at key off is the ISC resetting to 100% in anticipation of the next restart.

So it's just a poor design, and I would guess this is partly why they've moved to electronic throttle bodies and done away with ISCs (just like most modern cars).

Do you know of any workarounds like boscoe was trying to get at? I know I would like to prevent my ECM from frying if possible, but all I can think of at this point is: minimize idling as much as possible, regularly check the throttle linkage, keep the throttle bore & plate clean, and regularly check for YDS error codes related to the temp/pressure/TPS/pulser inputs.

[99yam40]

listen to your motor when you shut it off.
If you do not hear the rattle of the ISC,
then you have a stuck ISC and need to repair it as soon as possible

Also If you notice any problem with motor running or idling , do the same.

i would not think that would be very hard to think about doing, but then some folks think ,
I will just keep running it and hope it gets better

[rejesterd]

listen to your motor when you shut it off.
If you do not hear the rattle of the ISC,
then you have a stuck ISC and need to repair it as soon as possible

Also If you notice any problem with motor running or idling , do the same.

i would not think that would be very hard to think about doing, but then some folks think ,
I will just keep running it and hope it gets better

I can hear it rattle at the dock and the YDS tests for it pass, but I'm talking about proactive prevention, not observing and then reacting. This is clearly not a great design (as confirmed by a certified Yamaha master of puppets) so I was just wondering if it can be customized somehow. Seems like an appropriate thread to discuss it, as I don't think the OP ever presented an issue he was having.

[pstephens46]

listen to your motor when you shut it off.
If you do not hear the rattle of the ISC,
then you have a stuck ISC and need to repair it as soon as possible

Also If you notice any problem with motor running or idling , do the same.

i would not think that would be very hard to think about doing, but then some folks think ,
I will just keep running it and hope it gets better

Another option - sell the motor and possibly the boat and buy one with an electronic throttle body. Who can stand the thought of a failing ISC? Horror...

[rejesterd]

Another option - sell the motor and possibly the boat and buy one with an electronic throttle body. Who can stand the thought of a failing ISC? Horror...

Another option - Instead of bumping threads you think are boring, go help someone with an actual problem.