Volvo Penta 5.7 Gi-E IAC Issue

[quakana99]

Hello all,
I have an issue with my IAC opening the air flow to max on Idle. My boat neighbor has a Tech Mate pro and we can watch the IAC position reading eventually (after about 3 minutes) go to "0" which is allowing maximum airflow through the throttle body bypass chamber.

I replaced the IAC sensor and still have the same issue. It is causing the motor to rev up to about 2k RPM on the gauge and 1.5k RPM on the Tech Mate and also creates a horrible noise while the air is traveling through the bypass chamber.

In my simple mind, something is telling the IAC sensor to open up all the way and I am not sure where to look next.

Thanks in advance for any help.
Dave

 

[alldodge]

I don't understand the IAC at 0 and be full open
The IAC goes from 0 closed to 100 full open

Seeing 0 has me thinking its either a vacuum leak or TPS issue maybe
What does the Techmate show for TPS?
Have you tried disconnecting the throttle cable from the TB?

 

[quakana99]

Hello all,
I have an issue with my IAC opening the air flow to max on Idle. My boat neighbor has a Tech Mate pro and we can watch the IAC position reading eventually (after about 3 minutes) go to "0" which is allowing maximum airflow through the throttle body bypass chamber.

I replaced the IAC sensor and still have the same issue. It is causing the motor to rev up to about 2k RPM on the gauge and 1.5k RPM on the Tech Mate and also creates a horrible noise while the air is traveling through the bypass chamber.

In my simple mind, something is telling the IAC sensor to open up all the way and I am not sure where to look next.

Thanks in advance for any help.

I don't understand the IAC at 0 and be full open
The IAC goes from 0 closed to 100 full open

Seeing 0 has me thinking its either a vacuum leak or TPS issue maybe
What does the Techmate show for TPS?
Have you tried disconnecting the throttle cable from the TB?

Thanks! This is def odd because I have the spark arrestor off and when I initially install the sensor I pull the plunger out so that it is entirely plugging the hole. I use the throttle to give it a little air to start.

Then, I can hear the computer adjusting the IAC back and forth while the motor is running. The reading on the Techmate IIRC is around 66 + or - some while it is adjusting. After a few minutes the plunger starts to retract and the reading on the techmate quickly goes to 0 and the plunger retracts to where the hole is wide open. This is where the motor Revs up to 2k RPM
When you say "Closed" do you mean it is extended to the point where it's blocking all air ? I could be using the wrong terms

 

[alldodge]

Closed is plunger extended and cutting off all air

 

[alldodge]

Having to open the throttle some to start and then running that high you might have a TB or intake leak. The IAC is closing off trying to slow the idle down but its unable to

 

[quakana99]

Closed is plunger extended and cutting off all air

OK so there is def an issue I think with the signal the IAC must be getting.
I also replaced the TPC and it seems to read correctly on the tech mate while we put the throttle in neutral and give it some gas.
I have also noticed that sometimes the IAC works correctly until I give it some gas....and on returning the throttle to neutral.....the IAC opens back up again causing the Issue to return

Should I try running it again with TPC unplugged?

I have not disconnected the throttle from the TB but it def does not move when just at idle. It's def the IAC opening to let the hole be wide open. The suction through the hole in the throttle body (I am calling it a throttle body bypass chamber) is so intense it feels like it could suck my whole body through it lol. Appreciate the help and any advice.

I am wondering if its the computer

 

[quakana99]

Having to open the throttle some to start and then running that high you might have a TB or intake leak. The IAC is closing off trying to slow the idle down but its unable to

Well I am doing this on purpose. I pull the plunger out before I install as to plug the hole up and not let air through. The computer then adjusts it to let a little air in.....but eventually opens all the way up allowing 100% air flow.....but the techmate has the reading at 0. Sorry for the confusion

 

[alldodge]

Removing the throttle cable from the TB is done to make sure the cable is to make sure the TB is full closed. When motor starts put s little pressure to hold it closed to see if that makes a difference

Correct Techmate and turn key ON, don't start motor. Go to TPS position screen and should see close to zero% for position. Now move TPS to WOT to see if Techmate shows it goes full open.

If that works correctly, return TPS to idle and see what changes after the motor starts

 

[quakana99]

Removing the throttle cable from the TB is done to make sure the cable is to make sure the TB is full closed. When motor starts put s little pressure to hold it closed to see if that makes a difference

Correct Techmate and turn key ON, don't start motor. Go to TPS position screen and should see close to zero% for position. Now move TPS to WOT to see if Techmate shows it goes full open.

If that works correctly, return TPS to idle and see what changes after the motor starts

OK I will try this today.

So does the TPS and the IAC work together?
Also, any idea as to why if the IAC is wide open.....the techmate thinks it's closed ( at 0) ??

I am thinking since the techmate sees it at 0 and thinks it's closed.....so does the computer so maybe the computer has an issue?

Does the IAC typically go to 0 in normal operation after the motor starts and idles at correct speed or does it constantly move even while underway?

Thanks again for your replies and help. Appreciate it

 

[alldodge]

So does the TPS and the IAC work together?

Sort of, but its not working together, its sensors which tells the ECM what is happening. The TPS should be about 0.6V at idle and goes to about 4.5V at WOT. The IAC should be close to 40 counts (about 40%) at idle and go to zero when RPMs are above 1500

 

[quakana99]

Sort of, but its not working together, its sensors which tells the ECM what is happening. The TPS should be about 0.6V at idle and goes to about 4.5V at WOT. The IAC should be close to 40 counts (about 40%) at idle and go to zero when RPMs are above 1500

Disconnected the linkage. TPS was at 0. IAC stayed open but read "0" Boat revs up to 2k RPM. If I disconnect the TPS sensor it revs down to about 1200 RPM but the IAC does not move.

Even tried disconnecting the battery for 15 minutes to see if it would relearn and readjust the IAC but nothing.

I can manually move the plunger to get it where it runs ok but the ECM keeps adjusting it back to what it thinks is "0" but it remains open.....not closed for good after a few minutes

Everything else looks ok but there is a cam shaft sensor code 81 that keeps coming back..

Wondering if the ECM has gone faulty

 

[alldodge]

As first mentioned, the IAC should never read zero

I don't know what you have but if throttle plate is closed and if IAC was closed the motor should die

Most likely a vacuum leak

 

[quakana99]

As first mentioned, the IAC should never read zero

I don't know what you have but if throttle plate is closed and if IAC was closed the motor should die

Most likely a vacuum leak

The issue is......the IAC reads zero......but it's all the way OPEN.....meaning the plunger is all the way out of the hole and letting max air in through the hole in the throttle body which is why the motor is revving up. I can plug the hole with my thumb and the boat idles down

 

[alldodge]

I understand what your saying, but this should NOT happen. Its all the way open it should read 100

Did you get the wrong IAC or is there a wiring issue?

 

[quakana99]

I understand what your saying, but this should NOT happen. Its all the way open it should read 100

Did you get the wrong IAC or is there a wiring issue?

I do not think there is a wiring issue. This first happened while i was underway last saturday. When I was underway at about 10 MPH I backed off the throttle and put it into neutral....this is when it all started. The motor revved up and was the same symptom as I have had since so something is telling that IAC to open all the way up but its odd it thinks its closed.

I did not use a OEM volvo IAC but the one I ordered specifically mentioned it was compatible with Volvo Penta 3843750. I have also tried the old sensor and the same thing is happening

 

[alldodge]

The TPS should be about 0.6V at idle and goes to about 4.5V at WOT.

What is the TPS showing

 

[quakana99]

What is the TPS showing

I forgot to look at the voltage of TPS while running. But its odd if the TPS in unplugged the RPM's are no where near as high as when I plug it back in. about 800 RPM's high when I plug the TPS sensor plug back in

 

[alldodge]

I forgot to look at the voltage of TPS while running. But its odd if the TPS in unplugged the RPM's are no where near as high as when I plug it back in. about 800 RPM's high when I plug the TPS sensor plug back in

Techmate shows no codes
Unplug things and it runs better, but there are still no codes
IAC is working backwards and there are still no codes
No matter what is done like unplugging things which should throw codes do not

I have nothing, hope someone can help

 

[quakana99]

Techmate shows no codes
Unplug things and it runs better, but there are still no codes
IAC is working backwards and there are still no codes
No matter what is done like unplugging things which should throw codes do not

I have nothing, hope someone can help

Oh we get codes for low voltage on both sensors when we unplug them....there is a cam shaft position sensor 81 code that won't go away but that has been there all summer with no issue.

I am going to try another sensor and if that does not work I have a source that will test the ECM as I think something went bad in the computer.
Thank You for helping me out

 

[alldodge]

What the HE double hockey sticks? You have codes and thought that had nothing to do with your issue(s), good Greif

What low voltage codes?

If the 5V reference supply is low it may just be one of the sensors is drawing to much current. This issue happens often and can be found, but your thinking it has no bearing on the issue?