2g biss

MyBeatGSX · Jul 21, 2006

Has anyone done it or figured out a reliable, repeatable way to do it? I had horrible shaft seal leaks so I installed a 1G throttle body with new seals today. I started the car and it idled at 3,000rpm. Went back and checked under the hood... stupid me didn't plug the ISC back in. :coy:

But to no avail, I restarted the car and idle slowly came down to 2,000rpm where it stayed. I didn't want to touch the BISS because I knew the problems it was going to create. I didn't really have another choice though, so I screwed it in at least 10-20 full rotations. This brought it down to 800rpm. After much fiddling and tweaking, it now idles at 750rpm... most of the time. Its still not dead consistant like it used to be, and as I pulled into my garage which involves almost launching the car and then quickly stopping so I don't roll back over the cliff opposite my garage door or blast through my downstairs livingroom wall. Of course the car immediately died, which annoys me. It ran fine all night and I reved the crap out of it before leaving the house and it never stalled out once.

Bottom line, I need a way to adjust it without the scan tool. Trial and error doesn't seem to cut it. It either idles too high or stalls out, I can't seem to find a happy medium. Even when its was "working" for most of the night, idle is still fairly irratic. With my old TB it went between 720-760. It now goes anywhere from 680-820. IMO, I've driven it enough that ECU should have relearned the idle, it is using the same ISC after all....

I also did another boost leak test, there are no boost leaks so a vacuum leak isn't causing the problems. I do have a lightweight flywheel, I know I've heard of stalling problems before. However it never happened to me on the old TB so I don't see why it should start happening now.

TSIMonsteR · Jul 22, 2006

Is the ISC still good?

jabinya · Jul 22, 2006

I'm having the same problem as you. :notgood:

After I installed my 60mm TB I had no scan tool to set base idle with. I have been looking for a way to do it without the scan tool for a while. I have a laptop logger but no programs to hold the ISC while I adjust the BISS screw.

Eventually I have the BISS screw turned all the way in and it stays about 800rpms. Its a unstable idle for sure.

I suppose the local Mitsubishi dealership would set it but Im not giving up yet.

toojung2die · Jul 22, 2006

FWIW - A while back I attacked a bunch of small boost leaks around the intake. With a spray bottle of soapy water I found little leaks at the lower injector seals, t-body gaskets, t-body shaft, BISS screw, and many vacuum hose fittings. After eliminating all the leaks I learned that a little leak + little leak + little leak = Big Leak. When I finished and started my engine the idle was almost 2000 rpm after warm up. The proper way to set the idle rpm on a 2g involves using the MUT-II diagnostic tool. Not having one I counted the number of turns the BISS screw was at (2 turns out). I slowly turned the screw in and the idle rpm dropped. I left it at 3/4 turns out. The idea is to get the BISS screw set so the ISC is in the center of it's travel when the idle speed is correct so the ISC has the maximum range available to adjust the idle rpm. Without a MUT-II I have no way of knowing if my adjustment is optimum but for over a year now my idle has never been steadier. It's obvious my BISS screw had been adjusted in the past to compensate for the intake leaks. Have you done another boost leak test after changing the seals?

MyBeatGSX · Jul 22, 2006

Yes, as previously stated, I did another leak test right after I got done putting it all together. No leaks anywhere.

The thing that's hard to figure out, is that just because its idling at 750rpm, doesn't mean the ISC is in the middle. You could have the BISS closed just enough to get it to idle there and the ISC might be full out just to keep it there. Then you might adjust it what would be correct, but because the ECU is always trying to compensate the idle might not be even be at 750rpm right away. I also noticed the BISS is very touchy. But I'm going to go out there and play with it some more today.

jabinya · Jul 29, 2006

Any luck adjusting the BISS, MyBeatGSX?

MyBeatGSX · Aug 3, 2006

The other day I unplugged my ISC to see what it would do. There was no change in the idle. I readjusted my idle to 750-780rpm with the ISC unplugged and have had no issues running without it. It idles fairly steady (considering no ISC, its within 30rpm +/-) It doesn't even stall with the headlights on anymore. :confused:

Who needs an ISC. :thumb:

But I did order one anyway. I'm sure idle quality will be a different story in the winter.

toojung2die · Aug 3, 2006

MyBeatGSX said:
The other day I unplugged my ISC to see what it would do. There was no change in the idle. I readjusted my idle to 750-780rpm with the ISC unplugged and have had no issues running without it. It idles fairly steady (considering no ISC, its within 30rpm +/-) It doesn't even stall with the headlights on anymore. Who needs an ISC.

But I did order one anyway. I'm sure idle quality will be a different story in the winter.

I wonder if you haven't stumbled on a way to adjust 2g idle without the MUT-II? If you get your idle set by adjusting the BISS without the ISC then when the ISC is reconnected the ISC should be within it's desired range of adjustment by the ECU. It'll be interesting to see what happens when you get the new ISC on there...

1LE · Aug 3, 2006

Well, for those that might be reading this that have a '95, it's easy... For '96+, a MUT-II is the only "official" way, but if you can develop your own way, lots of people would appreciate it!

Anyways, quick overview for '95 owners (going completely from memory here, VERIFY with a manual before attempting! This is JUST a rough overview with some helpful hints!)...

1) Use a logger and find out how far off your stock tach is (Mine reads 850 when the ECU reports 750). VERY important for getting it just right! I didn't do this the first time, trust me, it's important!

2) Ground the timing plug (per the manual). Brown plug on the firewall, IIRC?

3) Ground the appropriate pin in the the OBD-2 connector. I THINK it was pin 1? VERIFY this with the manual! Once you do that, DOUBLE and TRIPLE check to make sure you understand which pin is the proper one on the plug! You can do a LOT of damage if you ground the wrong one! A MUT-II automatically grounds this pin when plugged in, but a standard ISO OBD-2 scanner does NOT!

4) Start up car and twiddle the BISS until you get your calibrated 750 rpms (on my car, a tach indicated 850).

5) Let car idle for 10 minutes to make sure it stays there.

6) Shut 'er down and unplug all your stuff! May still idle surge the first couple of trips as the ISC is NOT reset to 0 by the procedure (could be more trips if you're really incredibly far off I suppose?). It WILL have to relearn the ISC setting, but the new ISC setting will be right in the middle! You could try resetting the ECU to force a 0 ISC setting, but then your STFT and LTFT get whacked and that can cause issues too if your car is not 100% stock

I also use RTV to keep my BISS in place. The stock cap leaves enough gap that the BISS can back itself out some over time (just enough to mess up the idle).

FORMONTOYA · Aug 3, 2006

What worked for me when resealing the throttle body:

Plenty of "scripto" marks. Marked location of ISC before removal in 2+ locations.

Counted how many turns required to "soft" bottom of the BISS screw (for me it was 2 turns).

Then when reinstalling, align marks on ISC, "soft" bottom of BISS, then back out 2 turns. car idles at 750RPM and logs through DSMLink at 750RPM +/- 20RPM since Dec 2005.

pnishr · Aug 3, 2006

If you're going to do it the "ISC unplugged way" you'd need to make sure that the ISC is centered before doing so. Otherwise, you're just setting the idle with the ISC in it's current position, and it will still be in a "working" position. Perhaps putting the ignition in the "ON" position (which correct me if I'm wrong, makes the ISC re-find its center every time)- since you don't have DSMLink, THEN pull the connector. THEN start the car and set the idle. I don't see why it wouldn't work (assuming no leaks of course)

Or does the ISC re-center only with grounding?

Interesting. Hell, I've got DSMLink, and I'm still having issues with my idle sometimes. I DID have it fixed to perfect, but then I changed injectors and all of the sudden it sucks (using -40% global and 315 deadtime on FIC 750s) I may just remove the ISC and FIAV with a plate as somebody has done in another thread. Might as well try it.

zippyshoe · Aug 3, 2006

1LE said:
Well, for those that might be reading this that have a '95, it's easy... For '96+, a MUT-II is the only "official" way, but if you can develop your own way, lots of people would appreciate it!

Anyways, quick overview for '95 owners (going completely from memory here, VERIFY with a manual before attempting! This is JUST a rough overview with some helpful hints!)...

1) Use a logger and find out how far off your stock tach is (Mine reads 850 when the ECU reports 750). VERY important for getting it just right! I didn't do this the first time, trust me, it's important!

2) Ground the timing plug (per the manual). Brown plug on the firewall, IIRC?

3) Ground the appropriate pin in the the OBD-2 connector. I THINK it was pin 1? VERIFY this with the manual! Once you do that, DOUBLE and TRIPLE check to make sure you understand which pin is the proper one on the plug! You can do a LOT of damage if you ground the wrong one! A MUT-II automatically grounds this pin when plugged in, but a standard ISO OBD-2 scanner does NOT!

4) Start up car and twiddle the BISS until you get your calibrated 750 rpms (on my car, a tach indicated 850).

5) Let car idle for 10 minutes to make sure it stays there.

6) Shut 'er down and unplug all your stuff! May still idle surge the first couple of trips as the ISC is NOT reset to 0 by the procedure (could be more trips if you're really incredibly far off I suppose?). It WILL have to relearn the ISC setting, but the new ISC setting will be right in the middle! You could try resetting the ECU to force a 0 ISC setting, but then your STFT and LTFT get whacked and that can cause issues too if your car is not 100% stock I also use RTV to keep my BISS in place. The stock cap leaves enough gap that the BISS can back itself out some over time (just enough to mess up the idle).

If I'm not mistaken, I believe this method (grounding both the timing plug and the diagnostic pin of the OBDII connector) also works for the '96 model year. For DSMLink users, all you have to do is turn-on both the "GND Timing" and "GND Diag" buttons in the Miscellaneous box, which will simulate grounding these two points.

MyBeatGSX · Aug 3, 2006

At the moment I don't care how it worked. All that matters is that it did work. Even with the lights on I have no stalling issues and the idle drops very little. The only way I can even tell that the ISC is unplugged is that I don't have the higher coast down idle, which to me has made no difference in drivability. I should have save myself money and just keep running with no ISC.

If anyone wants to know how it was set... The car was fully up to temperature, I had just driven home from work. It was idling at (650rpm according to my AFC). I got out and unplugged the ISC, the idle did not change at all. I turned the BISS out <1/4 turn, checked back inside and it hovering between 740-780rpm. No complaints there. My car has an unrelated idle misfire that causes the fluctuation, so I have no complaints. My idle is back to how it was the old TB, minus the coasting compensation thing. I find this all kind of weird, because I was using the exact same ISC on my old TB with no problems at all.WTF :confused:

1LE · Aug 3, 2006

zippyshoe said:
If I'm not mistaken, I believe this method (grounding both the timing plug and the diagnostic pin of the OBDII connector) also works for the '96 model year. For DSMLink users, all you have to do is turn-on both the "GND Timing" and "GND Diag" buttons in the Miscellaneous box, which will simulate grounding these two points.

Yep, those would be the correct things to do with a DSMLink!

As far as the '96 goes, I don't know. I've heard that there are '96's out there with the brown timing plug, but I've also heard that at least on some of them that the plug doesn't actually GO anywhere. The official docs I can come up with suggest that '96 does NOT have that capability. However, who knows when changeover actually took effect

So, "maybe"?

bhop · Aug 7, 2006

Since this thread seems to have a lot of ISC talk....

How long does it take for the ECU to relearn after a new ISC and biss adjustment?

also, is this the 'brown' timing plug you are talking about 1LE? (mine looks more orange-ish, to the naked eye anyways, but could probably be considered brown) I've been trying to figure out what that loose plug is.

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1LE · Aug 7, 2006

bhop said:
Since this thread seems to have a lot of ISC talk....

How long does it take for the ECU to relearn after a new ISC and biss adjustment?

also, is this the 'brown' timing plug you are talking about 1LE? (mine looks more orange-ish, to the naked eye anyways, but could probably be considered brown) I've been trying to figure out what that loose plug is.

My car usually takes 4-5 cycles (start car, drive around for awhile, shut off car) to completely adjust after messing with those things (I would normally drive 20-40 miles per cycle).

That's the plug.

I think that little blue plug right behind it is where one can plug a precision tach in order to make setting the idle easier. Anyone know for sure?

bhop · Aug 7, 2006

1LE said:
My car usually takes 4-5 cycles (start car, drive around for awhile, shut off car) to completely adjust after messing with those things (I would normally drive 20-40 miles per cycle).

That's what I wanted to hear. I went for a short drive last night, and the rpms were still funky, but this morning it seems to be a little better. I'm hoping it's just going to take a couple days to settle down. I don't really want to spend more money on the black hole (my car's nickname since it sucks my wallet dry) right now.

I think that little blue plug right behind it is where one can plug a precision tach in order to make setting the idle easier. Anyone know for sure?

You're correct about the blue plug. Apparently it's for testing the engine speed.

daren_p · Sep 1, 2006

Did I read this correctly, my car is a 98 with DSMLink & I can properly set the BISS if I select ground timing & ground diag(sets ISC to 0?)? Currently my car seems to idle pretty good but I tried to select these 2 option & my rpms at idle dropped to high 500's--600. Does this mean that my BISS is abit out of adjustment or did I understand wrong?

1LE · Sep 1, 2006

daren_p said:
Did I read this correctly, my car is a 98 with DSMLink & I can properly set the BISS if I select ground timing & ground diag(sets ISC to 0?)? Currently my car seems to idle pretty good but I tried to select these 2 option & my rpms at idle dropped to high 500's--600. Does this mean that my BISS is abit out of adjustment or did I understand wrong?

That depends. The reference temperature for setting the BISS is 68F (if I remember correctly...). If it's 100F out, your idle will be lower. If it's 32F out, your idle will be higher, all with the BISS set properly... And of course, if you're at altitude, there's another variable

daren_p · Sep 3, 2006

Well I tried adjusting the BISS. Now since it has never been adjusted before & the car was stock when I got it, it would make sense that I have to turn the BISS out abit? (so the BISS will bypass more of the additional air Im now flowing) This is what I had to do, when I selected ground Diag & timing the idle dropped to around 600 so I backed the BISS out abit to get ~750. I guess we'll see what happens in a couple days.

I was wondering a couple things though, how much can the ISC vary the rpms? When I unplugged the ISC my idle rpms went up to ~1550. Another thing I noticed when I selected ground timing with dsmlink then logged it, the timing would stay at 5.2 deg. Now when I selected ground diag as well the timing would start to vary again?

fallenauthority · Sep 3, 2006

When i replaced my BISS o-ring a month or so ago i just unscrewed it replaced the O-ring and screwed it back in to roughly the depth it was at when i removed it and just adjusted it after i started it up without grounding anything and i always have a nice steady idle around 750-800. Maybe I got lucky?

Kevin Jewer · Sep 3, 2006

One point to remember, the ISC operates open loop, there is no feedback to the ECU on it's actual position. The only time the ECU will rehome the ISC is when it is reset. Whenever you unlpug the ISC with the motor running, you can pretty much guarantee that the ISC is now out of sync with the ECU

If you have DSMlink, simply log LearnedIdleAdj (long term) and ISCpostion (short term). When LearnedIdleAdj is 144, the BISS is set properly. ISC position will end up around 30.

The ECU adjusts the LearnedIdle slowly, especially in the closed direction.

daren_p · Sep 5, 2006

95GSXracer said:
One point to remember, the ISC operates open loop, there is no feedback to the ECU on it's actual position. The only time the ECU will rehome the ISC is when it is reset. Whenever you unlpug the ISC with the motor running, you can pretty much guarantee that the ISC is now out of sync with the ECU

Well I unplugged the ISC then started the car, let it run for abit to see what the idle did, shut the car off then plugged it back in. So sounds like my ISC may be out of sync? So it looks like I should unplug the battery to reset the ecu? then log the above mentioned items to adjust my biss correctly? These numbers that you have mentioned learnedidleadjust @ 144 & isc position ~30, do they have some kind of reference or scale? (ie how do you come up with these numbers?)

Kevin Jewer · Sep 5, 2006

Everything you mention is correct. The numbers were given by Dave Mertz of DSMlink, I would assume he got these values by studying the ECU code.

zippyshoe · Sep 5, 2006

For users of DSMLink, there are two methods of setting your base idle speed:

Method 1
1. Make sure engine is fully warmed-up and all accessories are off (A/C, fan, lights, etc.)
2. Select both "GND Timing" and "GND Diag" buttons in the Miscellaneous menu.
3. Log or monitor RPM's.
4. Carefully adjust BISS screw as necessary to achieve your target idle speed (factory default is 750rpm.) If you have selected an idle speed other than 750rpm in DSMLink, then adjust the BISS to achieve this new idle speed.
5. Make sure you de-select both "GND Timing" and "GND Diag" buttons when finished.

Method 2
1. Make sure engine is fully warmed-up and all accessories are off (A/C, fan, lights, etc.)
2. Log or monitor RPM's, LearnedIdleAdj, and ISCPosition.
3. Carefully adjust BISS screw a small amount.
4. Allow car to idle a few minutes and check LearnedIdleAdjust and ISCPosition values.
5. Go back to step 3 until you obtain LearnedIdleAdjust = 144 and ISCPosition ~ 30.

In either case, make sure you fix any and all boost leaks, especially after the throttle plate - otherwise, once you fix these leaks, you will need to re-adjust the base idle speed. Also make sure that IdleSw = 1 when idling (throttle plate is fully closed). Hope this helps! :thumb:

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