Iacv Causing A No-idle Issue - Please Read

[lexdud]

I would hope that the mods would allow this post to stay in the general forum as this venue will give this issue more exposure.

Many have posted procedures to remove and clean the valve ... with most people reporting excellent results. BUT ... but what if the problem is and is not being caused by your IACV? I know it sounds strange but please keep reading below:

II own a 1993 SC400 with 52,000 miles. A few months ago it would (every once-in-a-while) start idling very badly ... but this would clear up quickly by reving the engine to 2K RPMs for about 5 sec. Fast forward to 3 weeks ago ... the car runs ONLY when you give it some gas ... it will NOT idle at all.

I just bought a used IACV to replace my unit that I thought had gone bad. I replaced the outer part (with the motor and (cleaned) valve but the problem persists. Upon the first start-up my car will run BEAUTIFULLY forever, unless you turn the engine off. Upon restarting it the engine will run very rough with an idle speed of about 300 RPM. Turning the engine off again and restarting returns the car to it's original state ... it will NOT idle and only does so when the gas is pushed.

When I pull the IACV I always retract the valve so that it is in it's full open position when reinstalled. I believe that upon each subsequent start-up the valve is closing a bit until the 3rd restart when it completely closes ... and stays that way permanently. What I cannot figure out is why.

I was hoping that those endowed with more knowledge of how this system works could help. I believe that I now have two working IACVs and that the problem is probably what controls the valve to open and close. In my ignorance I am going to assume that it is the ECU.

Please chime in with any comments or advice you have. I do not like taking my car in for work as I like doing it myself. I am contemplating one or more of the following:

1) Taking the car into the stealership for a diagnostic.

2) Trying to find someone local to Orlando (UCF area) who has a '93 compatible ECU that I can borrow to check my theory.

3) Removing my ECU and sending it off to be repaired via a service I found on Ebay.

Thank you for reading ...

[SeanGrac]

I would hope that the mods would allow this post to stay in the general forum as this venue will give this issue more exposure.

Many have posted procedures to remove and clean the valve ... with most people reporting excellent results. BUT ... but what if the problem is and is not being caused by your IACV? I know it sounds strange but please keep reading below:

II own a 1993 SC400 with 52,000 miles. A few months ago it would (every once-in-a-while) start idling very badly ... but this would clear up quickly by reving the engine to 2K RPMs for about 5 sec. Fast forward to 3 weeks ago ... the car runs ONLY when you give it some gas ... it will NOT idle at all.

I just bought a used IACV to replace my unit that I thought had gone bad. I replaced the outer part (with the motor and (cleaned) valve but the problem persists. Upon the first start-up my car will run BEAUTIFULLY forever, unless you turn the engine off. Upon restarting it the engine will run very rough with an idle speed of about 300 RPM. Turning the engine off again and restarting returns the car to it's original state ... it will NOT idle and only does so when the gas is pushed.

When I pull the IACV I always retract the valve so that it is in it's full open position when reinstalled. I believe that upon each subsequent start-up the valve is closing a bit until the 3rd restart when it completely closes ... and stays that way permanently. What I cannot figure out is why.

I was hoping that those endowed with more knowledge of how this system works could help. I believe that I now have two working IACVs and that the problem is probably what controls the valve to open and close. In my ignorance I am going to assume that it is the ECU.

Please chime in with any comments or advice you have. I do not like taking my car in for work as I like doing it myself. I am contemplating one or more of the following:

1) Taking the car into the stealership for a diagnostic.

2) Trying to find someone local to Orlando (UCF area) who has a '93 compatible ECU that I can borrow to check my theory.

3) Removing my ECU and sending it off to be repaired via a service I found on Ebay.

Thank you for reading ...

Are you sure it's not a fuel problem?

[lexdud]

I would hope that the mods would allow this post to stay in the general forum as this venue will give this issue more exposure.

Many have posted procedures to remove and clean the valve ... with most people reporting excellent results. BUT ... but what if the problem is and is not being caused by your IACV? I know it sounds strange but please keep reading below:

II own a 1993 SC400 with 52,000 miles. A few months ago it would (every once-in-a-while) start idling very badly ... but this would clear up quickly by reving the engine to 2K RPMs for about 5 sec. Fast forward to 3 weeks ago ... the car runs ONLY when you give it some gas ... it will NOT idle at all.

I just bought a used IACV to replace my unit that I thought had gone bad. I replaced the outer part (with the motor and (cleaned) valve but the problem persists. Upon the first start-up my car will run BEAUTIFULLY forever, unless you turn the engine off. Upon restarting it the engine will run very rough with an idle speed of about 300 RPM. Turning the engine off again and restarting returns the car to it's original state ... it will NOT idle and only does so when the gas is pushed.

When I pull the IACV I always retract the valve so that it is in it's full open position when reinstalled. I believe that upon each subsequent start-up the valve is closing a bit until the 3rd restart when it completely closes ... and stays that way permanently. What I cannot figure out is why.

I was hoping that those endowed with more knowledge of how this system works could help. I believe that I now have two working IACVs and that the problem is probably what controls the valve to open and close. In my ignorance I am going to assume that it is the ECU.

Please chime in with any comments or advice you have. I do not like taking my car in for work as I like doing it myself. I am contemplating one or more of the following:

1) Taking the car into the stealership for a diagnostic.

2) Trying to find someone local to Orlando (UCF area) who has a '93 compatible ECU that I can borrow to check my theory.

3) Removing my ECU and sending it off to be repaired via a service I found on Ebay.

Thank you for reading ...

Are you sure it's not a fuel problem?

I am almost completely sure. The first time I start it after I remove/replace the IACV it will run forever (until the tank empties. I took the car to a local mech shop and they told me that they have no idea what was wrong with it ... but off-the-record would put bets on the IACV.

The IACV is causing the problem ... but not because it is broken.

[SKperformance]

low voltage being supplied to the IACV to retract it combined by carbon making it weak .

Just because it moves does not mean it works .

[lexdud]

low voltage being supplied to the IACV to retract it combined by carbon making it weak .

Just because it moves does not mean it works .

"... combined by carbon ..."? What do you mean? I cleaned the IACV and added anti-seize. So what is the solution?

[stcist2]

have you checked the quality of the ground supplied to the IACV? have you checked the voltage being applied by the ECM? ever heard of current ramping? I know it is used to help diag fuel pumps could also be used to check the current (amps) being used by the electric motor in the IACV ...It is possible that both the IACV valves are defective...I've even seen brand new dealer parts defective right out of the box!!!! May even need to eliminate the possibility that all of the other systems in the car are function normally by unplugging the IACV and create a controlled vaccuum leak; i used to have a fish tank air valve that i could control a vaccuum leak very precisely...my first guess would be the ground having a voltage drop(resistance)..check for voltage(millivolts) from the battery ground to the groung side of the plug to the IACV...just my two cents

oh and a link to current ramping here....>http://www.auto-video.com/current-ramping-p-14.html

[Oldtreemech]

I had similar problems after removing and cleaning the IACV several times. What appeared to work was a combination of adding a full can of Seafoam to the gas tank with additional fresh premium fuel and cleaning the IACV shaft and adding a Mobil One oil film to it to make it work smoothly. Clean the threaded stepper motor part of the shaft as well and add a film of Anti-seize or Mobil-One oil film. After cleaning and lubricating the shaft the spring on the shaft should freely spin the stepper motor and move the shaft to the forward or closed position. It solved a lot of my problems but occasionally have some misfires and hunting idle speeds but believe thats mostly bad fuel/water and needing a fuel filter change. Use some CRC Electrical Motor cleaner for the shaft and the stepper motor windings and Moving magnet on the shaft.

Once I put it back together it worked great. :)

[lexdud]

I had similar problems after removing and cleaning the IACV several times. What appeared to work was a combination of adding a full can of Seafoam to the gas tank with additional fresh premium fuel and cleaning the IACV shaft and adding a Mobil One oil film to it to make it work smoothly. Clean the threaded stepper motor part of the shaft as well and add a film of Anti-seize or Mobil-One oil film. After cleaning and lubricating the shaft the spring on the shaft should freely spin the stepper motor and move the shaft to the forward or closed position. It solved a lot of my problems but occasionally have some misfires and hunting idle speeds but believe thats mostly bad fuel/water and needing a fuel filter change. Use some CRC Electrical Motor cleaner for the shaft and the stepper motor windings and Moving magnet on the shaft.

Once I put it back together it worked great. :)

I paid the Lexus dealership $120 for a diagnostic. They told me that the IACV was bad as well as (possibly) the ECU. I have replaced the IACV and the car ran great for 10 minutes until the idle dipped. I turned the car off and then tried to restart it ... but it would not without the gas pedal being depressed.

So now I am back to square #1. Now I am looking for a used (good) ECU ... but there are MANY different versions of SC ECUs.

Lovely ...

[lexdud]

I had similar problems after removing and cleaning the IACV several times. What appeared to work was a combination of adding a full can of Seafoam to the gas tank with additional fresh premium fuel and cleaning the IACV shaft and adding a Mobil One oil film to it to make it work smoothly. Clean the threaded stepper motor part of the shaft as well and add a film of Anti-seize or Mobil-One oil film. After cleaning and lubricating the shaft the spring on the shaft should freely spin the stepper motor and move the shaft to the forward or closed position. It solved a lot of my problems but occasionally have some misfires and hunting idle speeds but believe thats mostly bad fuel/water and needing a fuel filter change. Use some CRC Electrical Motor cleaner for the shaft and the stepper motor windings and Moving magnet on the shaft.

Once I put it back together it worked great. :)

I paid the Lexus dealership $120 for a diagnostic. They told me that the IACV was bad as well as (possibly) the ECU. I have replaced the IACV and the car ran great for 10 minutes until the idle dipped. I turned the car off and then tried to restart it ... but it would not without the gas pedal being depressed.

So now I am back to square #1. Now I am looking for a used (good) ECU ... but there are MANY different versions of SC ECUs.

Lovely ...

I am adding a final post just in case someone ever has the same no-idle issue.

I finally solved my SC400 no-idle problem and this is how I did it:

I bought a used, working replacement ECU. The dealer cost for the ECU is $1,500. I bought one on-line for less than 1/10th that. Just remember to get the same model number ECU as the one in your car.