F115 IAC not receiving signal from ECU?

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2003 F115 with low idle/stalling between gears/low cold start RPM, ~650 hours on engine

I cannot figure this dang IAC valve issue... Ever since buying my boat the IAC has never worked properly.

I've can hear the IAC rattle on shutdown, so I know the IAC has power and is at least somewhat communicating with the ECU, at least as far as enough to know to reset when the motor is turned off.

but the IAC does not respond to any of the Active YDS tests even though YDS shows it should be opening and closing during the test, so we know the IAC is not actually doing anything while the motor is running

I've also got a very low idle and she will stall if I move the throttle too quickly from high revs to low or vice versa, I also do not get the cold start high RPMs, it just starts at regular ~700 rpm, all classic bad IAC symptoms

I've tried swapping in 2 new IAC valves, I've confirmed continuity on all wiring from IAC back to the ECU.

Only thing left that I can think of is the ECU itself is just not sending the signal to the IAC when requested??

Does anyone have any idea how to check that?

What else am i missing here? I cant find anyone brave enough to lend me their working ECU to test out.

Boat runs amazing other than this blasted IAC problem

 

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the idle in the youtube video was good at ~750 when I shot it a few months ago, but now that we are in the heat of summer it is idling at ~500-600, Im assuming from the 95F weather with 80% humidity and the IAC not doing a damn thing to adjust and allow more of this dense air in

 

[dingbat]

Diagnostic software is not a substitute for active troubleshooting. It tells you want is and isn’t happening, not why or why it’s not happening

Do you have a factory service manual?

Have you pulled the component(s) in question to bench test?

ECM stored any alarm or error messages?

Have you checked wiring integrity between the IAC and the CPU? A large percentage of EFI problems are voltage /wiring related

Checked for proper signals on the ECM connector back shell going to and from the component?

 

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th

Diagnostic software is not a substitute for active troubleshooting. It tells you want is and isn’t happening, not why or why it’s not happening

Do you have a factory service manual?

Have you pulled the component(s) in question to bench test?

ECM stored any alarm or error messages?

Have you checked wiring integrity between the IAC and the CPU? A large percentage of EFI problems are voltage /wiring related

Checked for proper signals on the ECM connector back shell going to and from the component?

thank you for the reply

yes, i have the FSM but it does not have much info on testing the IAC/ISC

I have pulled the ISC out and tried moving it with a 9v battery, I can get it to move slightly by jumping the coils, I also ohmed out the coils and they check out OK. I have also tried swapping it out with 2 other units.

I have checked all wiring going from ISC to the ECM with my voltmeter for continuity and all ohms out good

ECM does not show any errors

This is a 6 wire ISC valve, from what I understand, it has constant voltage provided to it and the driver in the ECM should be sending ground pulses to the coils to get them to move, but that does not seem to be happening

 

[dingbat]

This is a 6 wire ISC valve, from what I understand, it has constant voltage provided to it and the driver in the ECM should be sending ground pulses to the coils to get them to move, but that does not seem to be happening

Swapping the sensors pretty much eliminated the sensor.

You need to focus on the wiring (ground resistance -0 ohms) and or the input to the ECM to trigger the pulses.

Don't know if this is the specific valve in question, but they all work pretty much the same

 

[99yam40]

I do not think the temp of the valve should be that hot.
from what I have read in the past if the valve sticks and the ecu keeps trying to make it move it heats up and eventually over heats the ECU circuit that drives it causing that to fail also.

this is a stepper motor so it is not going to act like a regular motor when applying power