IAC stepper sticking closed (SOLVED!)

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rickb794
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IAC stepper sticking closed (SOLVED!)

Post by rickb794 »

I posted about this install previously (July) but did not find a solution

First close loop idle control works fine and this is an old install.

I am chasing an intermittent failure of the idle valve sticking closed with TS showing the idle motor is at 190 steps but the engine stalls and the valve is verified being closed solidly.
I can hear the motor start to idle slow and watch the stepper increase to the max stepping # in TS with no change to the idle speed.
30 - 40 percent of the time the motor idles at the commanded speed and 20 to 50 steps as it should, and you can see the steps moving 3 -5 steps either way to hold idle at target

>>>>> Can TS show the stepper has been driven 190 steps without the stepper chip actually sending power to the motor?

>>>>> Can 2 processors made years apart (1 new) have the same failure?

I have reflowed the solder joints of the jumper from S12C to JS9 and all 4 IAC jumpers.
I have verified 12v at pin 16 of the 40 pin processor socket.
I have substituted the motor and the processor with new parts.
I have ohmed out IAC1A IAC1B IAC2A & IAC2B they show no resistance between the motor and the MS.
After the stepper sticks I see no voltage at any of the 4 IAC motor wires and when I remove the motor from the body I find the pintle fully extended.
It’s like the stepper chip suddenly reverses and then shuts down after driving the motor fully closed.

Sometimes restarting the car will reset the IAC, it seems to be temperature related, it’s fine cold then goes from intermittent to solid bad as it heats up.

I ran a heat gun on the motor and monitored the resistance of the windings from the MS end of the harness and saw only a few ohms rise with considerable temp increase at the motor.
I am hesitant to use a heat gun in the processor, I am goig to try and find some freeze spray.

I can see 1 circuit wiring failing but not a total loss of power at the motor in both loops.
However when I switch the processor the fault still exists, then to spite me it starts working again after reinstalling the original processor.

>>>>> Does the stepper chip have thermal overload protection?
>>>>> Could the stepper motor pintle sticking overheat the stepper chip and cause it to shut down?
>>>>> Is there something else I am missing that is not processor related that can shut down the stepper chip?
Last edited by rickb794 on Sat Mar 31, 2018 9:31 am, edited 1 time in total.
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rickb794
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Re: IAC stepper sticking closed

Post by rickb794 »

MSQ attached
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Rickvolvo10-17.msq
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Matt Cramer
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Re: IAC stepper sticking closed

Post by Matt Cramer »

I'm going to answer all the questions first, then move into the area of recommendations.
rickb794 wrote:Can TS show the stepper has been driven 190 steps without the stepper chip actually sending power to the motor?
Yes - the processor sends out a set of pulses to the driver to command the valve to move, but has no features to verify that the stepper driver has actually sent power, nor can it verify that the power sent to the stepper caused it to move.
Can 2 processors made years apart (1 new) have the same failure?
It can, but the odds are pretty low. And a hardware failure is generally complete, not intermittent.
Does the stepper chip have thermal overload protection?
There is some limited protection there.
Could the stepper motor pintle sticking overheat the stepper chip and cause it to shut down?
This is somewhat plausible, but the chip generally doesn't stay shut down for prolonged periods of time.
Is there something else I am missing that is not processor related that can shut down the stepper chip?
Yes, here goes...

First, I'd do a hardware check with the IAC valve unplugged. Use output test mode - I/O to lock the IAC outputs on. When an output is on, its A pin will have 12 volts and its B pin will have zero. Turning the output off will give 0 volts on the A pin, and the B pin will have 12 volts on it IF the other output is on. See if you can get normal voltage behavior on all four pins.

Second, try increasing the step size; this will help with an unreliable valve. Try a 6 ms time step size and a 10 ms initial time step size. The valve will move slower but this can boost reliability if the valve is "sticky". 3 ms is rather low.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
rickb794
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Re: IAC stepper sticking closed

Post by rickb794 »

Thanks Matt, I will get the car back over here and post results.
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rickb794
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Re: IAC stepper sticking closed

Post by rickb794 »

Tried resetting the time step size as recommended.

"Try a 6 ms time step size and a 10 ms initial time step size."

No joy, had to raise base idle setting to prevent stalling.

Now after last trouble shooting session on the Boost controller http://www.msextra.com/forums/viewtopic ... 01&t=68115
the owner is complaining of a high idle.

I just can't seem to win with this car!
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Matt Cramer
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Re: IAC stepper sticking closed

Post by Matt Cramer »

Does the IAC output pass the voltage check?
Matt Cramer -1966 Dodge Dart slant six running on MS3X
rickb794
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Re: IAC stepper sticking closed

Post by rickb794 »

Is that check documented?
I know I've ohmed out the wires and the stepper will properly control the idle for a while.
Then the idle steps will start creeping up without a corresponding increase in motor speed till the steps eventually top out.
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Matt Cramer
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Re: IAC stepper sticking closed

Post by Matt Cramer »

Use output test mode - I/O to lock the IAC outputs on. When an output is on, its A pin will have 12 volts and its B pin will have zero. Turning the output off will give 0 volts on the A pin, and the B pin will have 12 volts on it IF the other output is on. See if you can get normal voltage behavior on all four pins.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
rickb794
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Re: IAC stepper sticking closed

Post by rickb794 »

Ah, will do.
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jamies
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Re: IAC stepper sticking closed

Post by jamies »

try putting the steppper in in/out test mode. let it run 10 mins or so then see how hot the driver ic and stepper are, to diaignose any thermal shutdown
rickb794
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Re: IAC stepper sticking closed

Post by rickb794 »

latest MSQ
Attachments
1-13-18.msq
(119.31 KiB) Downloaded 24 times
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
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rickb794
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Re: IAC stepper sticking closed (SOLVED!)

Post by rickb794 »

I reversed the hoses to the DIY Stepper Adapter. :yeah!:

https://www.diyautotune.com/product/cus ... iac-valve/

I found that the vacuum side was connected to the tip end of the valve.
When/if the valve closed or came close to closing engine vacuum would suck the valve closed.
The stepper motor does not have enough power to open the valve when it is held closed by vacuum.
The adapter is not labeled and I did not install it, so I can't take credit for that part.
I looked at another throttle body mounted stepper to see how they are plumbed and verified that vacuum opens the valve.

So if you ever do a remote stepper motor make sure the vacuum goes to the motor side and save yourself a year of head banging.
It would be nice if DIY included this vital info in the documentation for this product, or labeled the adapter.

Thanks for your efforts to help with a solution to this and I hope sharing the solution saves someone else from a dented forehead.
Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
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darkstarmedia
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Re: IAC stepper sticking closed (SOLVED!)

Post by darkstarmedia »

Thanks for the suggestion! I have been looking for ways to improve the packaging. I will look at having little slips printed and included in the the next run.

Richard
DarkStar Machine Works
richard@darkstarmachineworks.com
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Inline Idle Air Control Valve Housings now availible through Jerry at DIYAutoTune.com
dontz125
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Re: IAC stepper sticking closed (SOLVED!)

Post by dontz125 »

Perhaps something as simple as little return address stickers reading, "This side to engine" applied beside the appropriate port. The stickers don't need to be particularly rugged, and it doesn't matter if they fall off in service.
QuadraMAP Sensor Module -- PWM-to-Stepper Controller -- Dual Coil Driver
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turbo conversion
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Re: IAC stepper sticking closed (SOLVED!)

Post by turbo conversion »

I had the exact same problem on my first install with remote mounted pwm valve.

Don't know how I missed this post, I coud have saved you a lot of time and agrivation.

David
1976 Datsun 280Z L28ET Garrett GT35R T3-T04E stage3 50 trim 63 A/R housing custom grind cam 2000-6000 rpm 440cc injectors intercooled 18 lbs. boost
3" exhaust turbo back LC-1 o2 sensor Hallman manual boost controller EDIS 6 ignition batch fire 60mm throttle body 5 spd T5 borg warner 3.54 lsd
rickb794
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Re: IAC stepper sticking closed (SOLVED!)

Post by rickb794 »

My first post about that problem was July 2016!
turbo conversion wrote:I had the exact same problem on my first install with remote mounted pwm valve.

Don't know how I missed this post, I coud have saved you a lot of time and agrivation.

David
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Correctly identify your MS ecu here
Read the Do's and Don'ts to avoid the common pitfalls before starting your install or asking for help
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turbo conversion
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Re: IAC stepper sticking closed (SOLVED!)

Post by turbo conversion »

:oops: didn't catch the date.

David
1976 Datsun 280Z L28ET Garrett GT35R T3-T04E stage3 50 trim 63 A/R housing custom grind cam 2000-6000 rpm 440cc injectors intercooled 18 lbs. boost
3" exhaust turbo back LC-1 o2 sensor Hallman manual boost controller EDIS 6 ignition batch fire 60mm throttle body 5 spd T5 borg warner 3.54 lsd
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