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2G Cannot adjust ISC position to 30

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jkuga

Proven Member
140
29
Feb 12, 2017
Oregon
Alright Tuners, I have been dealing with an idle issue since I purchased my GSX in 2017. I am at a complete loss of what to do at this point.
Any advice is greatly appreciated.

My idle has always been sketchy. It feels like it has an intermittment misfire.
When I got the car it was surging. Along with other maintenance items that were changed when I bought it new o2 sensors were installed. This helped but it still is not right.
I have changed the plugs twice to BPR6ES's and new NGK wires as well. Plugs were gapped to 0.028.
I have followed the sigma six idle control guide and am at a loss on how to proceed at this point.
I cannot get my iscpos and learnedidleadj to 30 and 144.
I elimated all boost leaks I found from the throttle body gaskets, injector seals, and had my throttle body rebuilt by TMZ.
I also screwed the FIAV in all the way and elimated a large boost leak from the throttle body freeze plug.
My ISC reads about 42homs when tested which is within spec from what I have seen for a black ISC. I also tested it by turning the key and it does move.

My wideband is also reading around 15 afr at idle never oscilating around 14.7. I do not have it installed in the front o2 location but used a glowshift clamp on bung on my downpipe.
I just don't know what else to check. I want to get this right before moving on.

I have a log of my car up to temp with the BISS screwed in all of the way to get the idle down. But the ISC still won't adjust to the correct position. My tps reads correct at 0.63v.
If I have no boost/vacuum leaks, the isc is good, the FIAV is not a hidden problem, and my tps reads correctly what could be causing these problems?
I've uploaded a video of my wideband at idle and of the sound it makes which makes me think its missing. I've also attached a log.

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  • log.2020.06.03-05.elg
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Thanks for the fast reply. I suppose it's possible but unlikely. I had the 99 black box ecu in there stock until last month when I got ECMlink. I had them socket a 96 non eprom for me. Are there any visual cues that the drivers would be bad?
 
Looking at the log, the iscposition isn't maxing out in either direction which tells me it's just not adjusted correctly. Your iscposition is low at 13 so you need to turn the BISS screw in some more. In order to easily set the BISS, you need to reset the isc when the car is warm, as mentioned on six sigma, and immediately set the isc position. You can't screw around and let the car warm up or fix other issues. If you don't set the iscposition quickly, it can take a while to get it fully adjusted because of the relationship between iscposition and learnedidleadj. That's just my theory.
 
Wouldn't mind seeing what the old plugs look like might help. Mine idled like that once I got it back together, I double checked and seen my ignition timing was a bit off and I was running too rich. My wideband was jumping around like that until I got it lean enough, the line stabilized and so did my idle. I went through a couple sets of plugs getting it right. Im no expert but doesn't hurt to recheck the basics.
 
Looking at the log, the iscposition isn't maxing out in either direction which tells me it's just not adjusted correctly. Your iscposition is low at 13 so you need to turn the BISS screw in some more. In order to easily set the BISS, you need to reset the isc when the car is warm, as mentioned on six sigma, and immediately set the isc position. You can't screw around and let the car warm up or fix other issues. If you don't set the iscposition quickly, it can take a while to get it fully adjusted because of the relationship between iscposition and learnedidleadj. That's just my theory.

Thank you for your theory. That could be a possibility as I did not disconnect the battery after warming the car up. I simply went straight into trying to set it.

Wouldn't mind seeing what the old plugs look like might help. Mine idled like that once I got it back together, I double checked and seen my ignition timing was a bit off and I was running too rich. My wideband was jumping around like that until I got it lean enough, the line stabilized and so did my idle. I went through a couple sets of plugs getting it right. Im no expert but doesn't hurt to recheck the basics.

I will get a picture of the plugs later they were a bit black on the tips and were less than 10k old. As far as I have been able to find I though 2g ignition timing was set and none adjustable? Glad you were able to figure yours out. This has been driving me crazy for a while now.
 
Thank you for your theory. That could be a possibility as I did not disconnect the battery after warming the car up. I simply went straight into trying to set it.



I will get a picture of the plugs later they were a bit black on the tips and were less than 10k old. As far as I have been able to find I though 2g ignition timing was set and none adjustable? Glad you were able to figure yours out. This has been driving me crazy for a while now.
Some people, including myself, have had misfires with new ngk wires. Not sure if the problem persisted through 2 sets of wires though.
 
I keep a new set of no name plug wires (RockAuto $5) around just to test with after my NGK wires started acting all goofy and they were only about 6 months old. A new set of wires fixed my issue. They were arcing to my hood. Just my experience.
 
Wouldn't mind seeing what the old plugs look like might help. Mine idled like that once I got it back together, I double checked and seen my ignition timing was a bit off and I was running too rich. My wideband was jumping around like that until I got it lean enough, the line stabilized and so did my idle. I went through a couple sets of plugs getting it right. Im no expert but doesn't hurt to recheck the basics.

Here are some pics of the old plugs with about 6,000 miles on them.
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It's seems like the isc position and slight miss are separate issues.
I will reset the ecu and try and set the biss correct again.
And I will order up some new plug wires and see if that helps with the miss.
Would the lean wideband reading be from having the biss/isc out of wack?

Looking at the log, the iscposition isn't maxing out in either direction which tells me it's just not adjusted correctly. Your iscposition is low at 13 so you need to turn the BISS screw in some more. In order to easily set the BISS, you need to reset the isc when the car is warm, as mentioned on six sigma, and immediately set the isc position. You can't screw around and let the car warm up or fix other issues. If you don't set the iscposition quickly, it can take a while to get it fully adjusted because of the relationship between iscposition and learnedidleadj. That's just my theory.

I don't know if this means anything but I had my BISS all the way in when I took the log. I'm going to reset the ecu and try again right now.
 
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If your BISS screw is all the way in, then something's still not right. More vacuum leaks maybe?... Have you adjusted the throttle stop plate...? I've been messing with my BISS setting and throttle stop setting for a couple months....Unfortunately I don't have DSM link yet....

I believe the correct way to reset the ECU for the idle is to:
1) warm up the car fully, then turn it off.
2) Disconnect the battery (negative terminal is best to avoid any issues), wait a couple minutes for the ECU memory to be erased.
3) reconnect the battery
4) start the car
5) adjust the BISS within 30 seconds to 750rpm. After that, the ECU starts making compensation with the ISC motor, making it difficult to get it centered.

And if you have mods like bigger cams, bigger throttle body, front mount intercooler and piping, open element air cleaner etc....it all has to be factored in...the factory service manual procedures may not work as well...and its a PITA trying to do it all without the proper diagnostic equipment. But you are using the DSM link so hopefully your path will be easier than mine has been!
 
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If your BISS screw is all the way in, then something's still not right. More vacuum leaks maybe? Have you adjusted the throttle stop plate...? I've been messing with my BISS setting and throttle stop setting for a couple months... Unfortunately I don't have DSM link yet....
I believe the correct way to reset the ECU for the idle is to:
1) warm up the car fully, then turn it off.
2) Disconnect the battery (negative terminal is best to avoid any issues), wait a couple minutes for the ECU memory to be erased.
3) reconnect the battery
4) start the car
5) adjust the BISS within 30 seconds to 750rpm. After that, the ECU starts making compensation with the ISC motor, making it difficult to get it centered.

And if you have mods like bigger cams, bigger throttle body, front mount intercooler and piping, open element air cleaner etc....it all has to be factored in...the factory procedures may not work as well...and its a PITA trying to do it all without the proper diagnostic equipment. Hopefully your path will be easier than mine has been!

It's been a pita so far haha so I can sympathize with you there. I can get the idle to ~750 but that is with the biss closed and the isc at 0 and learnedadj at 123 or so. I'm going to disconnect the battery and then restart with the biss closed and see if the isc will read higher than 30 for a steady period of time. It has been reading low 0-13 consistently so I'm not sure. It seems that it will drop well below 30 even with the biss closed and then I cannot get it above to attempt to adjust with the biss.
Ive checked for boost leaks a hundred times but I will do that again in the next few days. But the throttle seals, throttle gaskets, cruise cable, intercooler pipes, and intake manifold gasket are all good. So I honestly don't expect to find any leaks.

I have got two logs here. The first is after the ecu was reset with the biss opened two full turns from shut. The iscpos drops throughout the log until it is at zero. Idle is right at 750 but the isc would still need to be have a range to operate from that starting point which it does not if it is at zero right?
The second log is with the ecu reset and the biss turned all the way in. It starts at about 30 but continues dropping from there. Any thoughts?
 

Attachments

  • log.2020.06.04-01.elg
    147.5 KB · Views: 66
  • log.2020.06.04-04.elg
    145.3 KB · Views: 70
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Does the ISC motor move both ways?? I wouldn't overlook a bad driver in the ECU.

Did ya check the movement of the ISC in/out and also for weak spots in the movement? Seems a little strange it always goes to zero position or maybe its fighting a throttle stop that's set slightly too far open...?

Is the idle still surging? If the BISS screw is set all the way closed and the ISC is all the way closed at zero, that means too much air is getting past the throttle plate somewhere....

By the way, in your video, your car idles 100% smoother than mine does with the big cams in it and no DSM link! I would be happy if mine idled as smoothly as yours LOL!
 
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By the way, in your video, your car idles 100% smoother than mine does with the big cams in it and no DSM link! I would be happy if mine idled as smoothly as yours LOL!

Haha to be fair its all stock essentially so I would hope it would idle better without the big cams. The idle isn't terrible I would just like to figure out what the little skip it seems to have is. But it does idle at 750 rpm which is better then it was at the start of the year so I suppose I should be happy with that!
As far as ISC drivers go I have had the stock black box ecu in it and just put in a chipped one from ECMlink. There were no visual cues that anything was burned out or bad on the chipped ecu but I will reach out to ECMLink to see if it is something that gets checked or maybe I will send it in. The isc test right as far as resistance goes and it moves in and out when the power is turned on and off with it unplugged. I've tested it warm and cold.
If my wideband is reading lean and it always zeroes out I guess you are right that air is getting in somewhere. I had TMZ rebuild my throttle body but I don't know that the throttle stop screw was touched. Another thing to check I suppose.
Time for more leak testing but it feels like an exercise in futility haha.
 
Did anybody mention the throttle cable? Is the throttle fully shut?
I adjusted the throttle cable as follows:
Loosen the adjustment bolts on the throttle cable bracket.
Have a friend floor the gas pedal. Be sure there are no floor matts or other obstructions in the way.
Pull the throttle cable jacket/bracket back until the throttle is open against the WOT stop, and hold it there.
Tighten the adjustment bolts to lock it down.

I do believe it was open before because of this but there is quite a bit of slack now.
 
Those plugs seem way to clean, would of like to seen a little more brown on em. Does your car still have the egr valve? if yes maybe its stuck open, if no maybe your getting some leaking around that area. My first block off plate I bought didn't seal right, I than made my own out of thin sheet metal, and bolted the egr back on.

https://www.ecmtuning.com/wiki/idlesur

It says the ecu will cut injectors to attempt to get the idle stable, that would make sense for the abnormal afr and why the plugs look the way they do, doesn't really fit for the smooth idle but hey maybe its a minor leak on one of those things. If anything I found it a interesting read.
 
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My guess is the throttle plate isn’t centered. When you rebuild the tb and take the stop out completely the throttle plate will stick shut. It will also stick shut prematurely if the plate is even remotely off centered. When being rebuilt, it’s possible they were in a hurry and after the plate stuck, they just bumped the throttle stop a hair to keep it from sticking. Regardless, if the BISS is all the way in and the isc won’t budge, you’re getting too much air past the throttle plate.
 
Those plugs seem way to clean, would of like to seen a little more brown on em. Does your car still have the egr valve? if yes maybe its stuck open, if no maybe your getting some leaking around that area. My first block off plate I bought didn't seal right, I than made my own out of thin sheet metal, and bolted the egr back on.

https://www.ecmtuning.com/wiki/idlesur

It says the ecu will cut injectors to attempt to get the idle stable, that would make sense for the abnormal afr and why the plugs look the way they do, doesn't really fit for the smooth idle but hey maybe its a minor leak on one of those things. If anything I found it a interesting read.

Good to know the plugs looked ok. I did just recently block off the egr and the plate leaked a little but that leak has been plugged with an open gasket and some rtv. That is a good read I forgot it had that list of things to check for leaks. At the very least I can double check all of those.

My guess is the throttle plate isn’t centered. When you rebuild the tb and take the stop out completely the throttle plate will stick shut. It will also stick shut prematurely if the plate is even remotely off centered. When being rebuilt, it’s possible they were in a hurry and after the plate stuck, they just bumped the throttle stop a hair to keep it from sticking. Regardless, if the BISS is all the way in and the isc won’t budge, you’re getting too much air past the throttle plate.

I will try and adjust the stop and see if that will make any change. If the plate is off center would the throttle body have to be disassembled and reassembled to make sure it was correct? Maybe something to try as a last resort.
 
I will try and adjust the stop and see if that will make any change. If the plate is off center would the throttle body have to be disassembled and reassembled to make sure it was correct? Maybe something to try as a last resort.

You would have to loosen the plate screws slightly and let it snap closed a few times then tighten them back up. I have also overtightened the cable pulley a time or two and found it added restriction to the throttle so you may also check that.
 
You would have to loosen the plate screws slightly and let it snap closed a few times then tighten them back up. I have also overtightened the cable pulley a time or two and found it added restriction to the throttle so you may also check that.
Alright I have been continuing to fiddle with the biss and can get the idle down to 750 but the biss is completely closed and the isc is operating from 0-10 at idle. I took my throttle body off and have not yet attempted to unscrew the plate screws or change where the stop is.
Before I do:
Does it look like the throttle plate is too open where the stop screw positioned right now?
Am I supposed to be able to see light around the plate?
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That doesn’t look flat to me and does look to be slightly open. It’s either not centered or you over tighten the nut for the shaft.

The nut for the shaft being the nut on the back of the pulley?
So first step then is to try and center it by loosening the plate screws and letting it snap closed then tightening them down.
 
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