Resolved Basic ISC Questions

[habitatguy187]

I’ve spent over an hour searching for simple answers I can’t find, so here goes:

ISC position reading 0 means that it is fully closed? (Trying to lower idle)??

Default ISC start position is 30?

How do move the ISC back to default position? By unplugging it or unplugging the battery or both?

I’m trying to tune a car that’s idling high but the ISC is reading 64-100 (calling for more air??)

 

[99dsmer4g63]

I believe when you turn the key on with the ISC plugged in you should hear it start clicking which is the stepper motor moving to its furthest position. It does this so the ECU knows where the motor is and is it’s starting point.

I don’t think 30 is it’s default position but with no vacuum leaks and the BISS screw adjusted properly that is where you want it to hover.

You can also pull the ISC and test it with an ohm meter and see if it’s within spec if you suspect it to be faulty. You can also use a 6v camera battery and hook it up to the ISC and bench test it to ensure it is stepping appropriately.

Also this is information for a 2g not sure how it translates to a 1g. Sorry that’s all I got for you

-Daniel

 

[SixBolt_16G]

hmmm... I just fixed my idle a couple of weeks ago. I can confirm that disconnecting the battery will reset the "lrnidleadjust" value to 144 which is default but will not set the "isc position" to 30 because as @99dsmer4g63 said, its not a default.

I waited for the car to warm up to operating temperature and waited for the radiator fan to turn off, then turn the BISS screw til I reached 29/30. It was bouncing a bit. Checked it yesterday again and it was sitting at 30.

But make sure you do a boost leak test so that you don't have a vacuum leak, or all the idle tuning you're trying to do will be irrelevant.

 

[99dsmer4g63]

Figured I’d add some more as I thought about it after posting. It is important to ensure there is no vacuum leaks. Adjusting the BISS with vacuum leaks is just masking the vacuum leak.

As said by @SixBolt_16G if the vacuum leaks are sealed up wait to adjust the BISS until the vehicle is at operating temperature. When I didn’t have link I turned the BISS screw all the way shut and then backed it out to about 2 - 2.5 turns. This got me pretty close. Sounds like you have DSMLink though so you can monitor it to get to hover around 30.

-Daniel

 

[habitatguy187]

So when the ISC position reads 75, it is allowing MORE air in correct? 0 means that it’s fully closed?

0 means it’s trying to lower idle and 100 means that it’s trying to raise idle, correct?

 

[SixBolt_16G]

So when the ISC position reads 75, it is allowing MORE air in correct? 0 means that it’s fully closed?

0 means it’s trying to lower idle and 100 means that it’s trying to raise idle, correct?

0 would be fully closed.

When I started trying to tune my idle it was around 70 something I believe. Trying to turn the BISS was doing nothing because I had air coming in from somewhere else. I had leaks at my boost gauge hose, throttle body gasket, and air pouring out of the BISS screw itself because the o-ring was shot, so all these leaks were adding more air into the system.

If you're at 75 and turning the BISS isn't working, then it definitely sounds like you have air coming in from elsewhere aka boost/vacuum leak. If that still doesn't help the issue, (after doing a little research, not off the top of my head), you might have to pull your ECU and check for damage to the ISC drivers.

I've only tuned idle with ECMLink once, so I'd concede to someone whose had more experience, but this is how things when for me since I just did this within the last 2+ weeks.

Can you at least confirm that you don't have any leaks? This is the most important thing because like I said previously, if you have leaks, then there's no use in trying to tune the idle until those have been resolved.

 

[habitatguy187]

I can't confirm personally as the car is not here.

I guess now my question is, if the vehicle is idling above target idle, why would the isc read 65-100 and not something closer to 0? Doesn't the ecu instruct the isc to close when the throttle stop switch is activated and idle is above target? From what I've gathered, it appears that this ecu is not instructing the isc to close.

 

[steve]

I guess now my question is, if the vehicle is idling above target idle, why would the isc read 65-100 and not something closer to 0?

Doesn't the ECU instruct the ISC to close when the throttle stop switch is activated and idle is above target? From what I've gathered, it appears that this ECU is not instructing the ISC to close.

Yes, if the IPS is closed the ECU should be closing the ISC position to bring the idle down. This assumes the car is fully warmed up. Not closing the ISC to 0 but to the normal place of about 30 steps.

Since the ISC doesn't provide direct feedback of it's position a step value of 0 means the ECU is trying to lower the idle speed and can't and going to about 120 or so means that the ECU can't raise the idle speed an and maxed out. (max steps varies between ECU years)

Get a good log of it doing this. Maybe that will answer the questions or pose more.