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2G ISC working backwards

mattsGSTeclipse

15+ Year Contributor
204
8
Dec 20, 2005
Lewiston, Maine
Hey guys,

My ISC has been having issues for awhile and I'm really trying to fix it now to get this car working right. The ISC will retract when the key is turned to the ON position after shutting off power for at least 30 minutes, rather than fully extend. So far I've swapped ISC, checked the two center red wires with no power for continuity and 12v power with the key ON, which was fine, visually checked each of the 6 wires to make sure they are in the correct spots and toned them out from the connector to the ECU, which was good. The car is wire tucked with a custom harness but since the wires checked out fine I don't see that being the issue. Could it be an ECU issue? What else should I check?
 

steve

DSM Wiseman
14,856
1,718
Feb 3, 2002
Boulder, Colorado
The ISC will retract when the key is turned to the ON position after shutting off power for at least 30 minutes, rather than fully extend.

What makes you think it parks extended?

In this video the last time he turns off the power before the cycle is finished but watch the two other cycles and see where the ISC finishes before he restarts the ECU again.

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We're on Boost

15+ Year Contributor
1,592
416
Aug 25, 2007
Seattle area, Washington
The ISC will retract when the key is turned to the ON position after shutting off power for at least 30 minutes, rather than fully extend.

Yes, that is how it is supposed to work when you are testing it with the engine not running. When you turn the key on, the pintle retracts. When you turn the key off, the pintle extends again.
I had to look into this in a big way to get a 1991-and-newer ISC to work correctly with a 1990 ecu. While doing that we found one little extra trick it does, which I only noticed by taking measurements of the pintle extension, and taking accurate video of it and looking at it frame by frame in a video editor. If you're interested in that, you can read post #8, 9, and 10 in this thread:

The video is here - be sure to open the video description (Show More) and read it, because it explains the timeline of the video.
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We're on Boost

15+ Year Contributor
1,592
416
Aug 25, 2007
Seattle area, Washington
Hmm why does every how to that I've read about ISC operation say that it will fully extend then retract slightly? if its working correctly?

For all I know there might be some makes of cars that do it that way.

But what I've seen by doing engine-off testing with the ISC out where you can see it, combined with looking at a log that goes from cold start to shut-off at the end of a drive, it's like this:

After driving for a while, the ISC position at idle will be near 0. Could be 0, 10, 20, 30, something like that. So at the end of your drive with the car idling just before shutting it off, it's near 0. When you shut the engine off, the log shows the ISC position going to 90. That is retracting. That retraction from 0 to 90 takes about 1 second, after you turn the key to Off. Then a few seconds later the MPI relay switches off, with the ISC still at 90.

Then next day you cold start to go for a drive again, logging the cold start. You turn the key to On, then you start logging, by the time the log is running the ISC is at 120. So apparently it retracted from 90 to 120 right after you turned the key to On. Then you turn the key to Start. And as the engine warms up the ISC position will slowly trickle downward towards 0 again.

It might be that some car makers might do what you are saying during that time right after key-on when ours goes from 90 to 120. I'm pretty sure ours doesn't, because that part of it you can see by taking the ISC out and looking at it during key on without starting the engine, like we did in the 2 videos above.

Doing it the way you suggested might be how some car makers get the ISC to re-zero itself. Calibrating the "0" point. When the pintle runs into the valve seat it can't go any farther. If the ECU says at that time, ok we're at 0, then the ISC has re-calibrated itself.
On ours, I don't know for sure but if you read posts #8, 9 and 10 in that other thread I linked to, we saw the pintle make a very small unexpected extend move that we figure might be how ours re-zeros itself, maybe gradually, or whatever, I don't know.
 
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We're on Boost

15+ Year Contributor
1,592
416
Aug 25, 2007
Seattle area, Washington
So basically, the ISC wants to be at 90 whenever the key is Off.
It wants to go to 120 when you turn the key On with a cold engine.
Then if you don't actually start the engine, if you just turn the key back off, the ISC will go back to 90.
That's what we are seeing in the 2 videos. We're seeing the ISC go back and forth between 90 and 120.
 

mattsGSTeclipse

15+ Year Contributor
204
8
Dec 20, 2005
Lewiston, Maine
For all I know there might be some makes of cars that do it that way.
I'm only talking about DSMs here. This info is straight from the ECMtuning website and other trusted websites I've seen that discuss DSM ISC operation and testing.
Forget about the expending and retracting. What exactly is the problem you're having and post a log of it.
The car has never ran correctly under its current configuration, I've had it dyno tuned twice and both times never got thru a full tune due to issues(plus the tuner sucked and didn't care). I'm trying to fix and test every possible issue that could come up. The car doesn't idle right and never has. I can post a log later when its drive-able.

I've got a magnus remote mount ISC adapter if it matters.
 

Vegas Smith

15+ Year Contributor
5,031
2,901
Dec 2, 2002
Houston, Texas
I'm only talking about DSMs here. This info is straight from the ECMtuning website and other trusted websites I've seen that discuss DSM ISC operation and testing.

The car has never ran correctly under its current configuration, I've had it dyno tuned twice and both times never got thru a full tune due to issues(plus the tuner sucked and didn't care). I'm trying to fix and test every possible issue that could come up. The car doesn't idle right and never has. I can post a log later when its drive-able.

I've got a magnus remote mount ISC adapter if it matters.
That doesn't help at all. Saying the car doesn't idle right means nothing.
 

We're on Boost

15+ Year Contributor
1,592
416
Aug 25, 2007
Seattle area, Washington
This info is straight from the ECMtuning website and other trusted websites I've seen that discuss DSM ISC operation and testing.

It sounds like you are talking about how the wiki says it is supposed to act after doing an ECU Reset.
From the ECMTuning wiki:
Turn off the ignition and reset the ECU by removing battery backup power for at least 10 seconds, then restoring battery backup. Then, with the ISC unbolted from the throttle body but plugged in to the wiring harness, turn on the ignition and observe the movement of the ISC. The ISC should fully extend, then retract slightly.
http://www.ecmtuning.com/wiki/idlesurge

In my posts above and in the 2 videos posted, we are not talking about doing this after an ECU reset. The 2 videos are just showing normal operation without having done an ECU reset first.
 

mattsGSTeclipse

15+ Year Contributor
204
8
Dec 20, 2005
Lewiston, Maine
In my posts above and in the 2 videos posted, we are not talking about doing this after an ECU reset. The 2 videos are just showing normal operation without having done an ECU reset first.
I'm talking about after doing an ECU reset. I'm starting from the beginning and making sure it works after resetting the ECU. My ISC is not acting correctly after an ECU reset. So why should I assume its working correctly other times?
 

We're on Boost

15+ Year Contributor
1,592
416
Aug 25, 2007
Seattle area, Washington
If your ISC is not acting right and it's actually giving you running problems, then you are correct to keep looking into it to figure it all out. I won't be able to help you with how it is supposed to act after an ECU reset because I have never bothered to try to verify that.

I noticed that @rabenne had a similar question going with this, and at the end of the thread he still had the question sort of unresolved. Here's a link to that thread in case you want to see what he went through. Maybe he could chip in here to let us know if he ever resolved that question any farther. You could almost just read posts 44 and 45 in his thread:
https://www.dsmtuners.com/threads/r...ought-the-issues.510124/page-2#post-153632232

The magnus remote mount ISC adapter, oh I see, looks like you run the idle air through hoses. Man I don't know.

But I think you'll also need to show us with logs or some way, what is actually wrong with how the car is working.
 
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