1G How far out/in should BISS generally be on a stock 1G turbo?

[XC92]

I've been having idle surge issues and have begun the process of diagnosing and fixing it. The idle position switch seemed iffy with the cable about to snap off so I fixed that, but it didn't fix the surge issue. Next steps are to remove and clean the throttle body and idle control servo and replace all the gaskets and o-rings, check for vacuum leaks, test all the applicable sensors and check the connectors and wires, and so on. You know the drill.

But I thought I'd first check the BISS, and it seemed to be turned pretty far out. It took 5 or 6 complete turns to go all the way in. Is that normal? I turned it all the way in, then back it off half a turn or so, and the surge appeared to go away, although granted I haven't driven the car and let it get up to temp. But idle is now around 800rpm, where before even without surging it was well over 1000rpm, and when it surged it cycled between 1200-1400rpm once it got up to operating temp.

Have I potentially fixed the issue, or just masked it? I had suspected that it was actually a bad or stuck ICS, and still intend to clean and check it both electrically and mechanically, but could this have actually been the problem?

 

[Lucky13]

Most guides for dealing idle surge tell you to screw the BISS all the way in and then back it out a half to full turn to start. So if that basically worked for you.....maybe the BISS was just out of adjustment.
http://www.vfaq.com/mods/BISS-1G.html

Do you have access to any tuning software that would let you log the ISC and see where it's at and how it's acting? There are a couple learned settings that take time to settle in every time you adjust the BISS. I know there is a guide around here somewhere with ISC steps around 30 at idle and a learned adjustment of around 140. Watching this if figured out my ECU was damaged after testing multiple ISC's for functionality.

Found the guide...

https://www.dsmtuners.com/threads/basic-dsmlink-tuning-guide.262460/

 

[XC92]

It was way out, at least 5-6 turns. Not sure how that happened. I never touched it so either it vibrated out or some mech who messed with the engine did it ages ago and I just haven't paid attention, or it wasn't so bad until recently. The cap is gone so I wonder if that made it possible for it to vibrate out? And I don't have diagnostic SW. At some point I'll get it but it's not a huge priority now since I'm not looking to tune anything quite yet and things are more or less running ok, just this idle surge issue.

 

[DSMPT]

If vibration turns the BISS, then you may have leak from there, it's probably time to replace its seal (o-ring). As long as the o-ring is healthy, the BISS shouldn't be turned by vibration.

 

[XC92]

I'm basically going to replace all the maintenance replacement items, gaskets, o-rings, seals, hoses, etc. It's time. 30 years does its thing.

 

[waltah]

It was way out, at least 5-6 turns. Not sure how that happened. I never touched it so either it vibrated out or some mech who messed with the engine did it ages ago and I just haven't paid attention, or it wasn't so bad until recently. The cap is gone so I wonder if that made it possible for it to vibrate out? And I don't have diagnostic SW. At some point I'll get it but it's not a huge priority now since I'm not looking to tune anything quite yet and things are more or less running ok, just this idle surge issue.

Most Mitsus I've run have had those adjustments fooled with by someone who didn't know what they're for -- my avatar car BISS was a couple turns out from correct. If a half turn setting got rid of the surge that's probably your problem. 5-6 turns is wrong.

The reason to get some kind of logger or tuning tool is that the BISS screw provides the basic idle air. When it's set correctly the ISC then has the range to handle fast idle in very cold weather so you don't stall on starting, the dashpot function when you take your foot off the pedal suddenly, 'idle up' for accessory loads. It is possible to tweak BISS watching how that other stuff behaves but it's just a lot quicker to know how many ISC steps you've got when the car is warmed up in normal weather without accessory loads. Steps too low = turn the BISS in 1/8 turn and test again ... etc.

In other words this is a basic engine adjustment issue -- not really 'tuning' as the word is mostly used here.

 

[XC92]

Most Mitsus I've run have had those adjustments fooled with by someone who didn't know what they're for -- my avatar car BISS was a couple turns out from correct. If a half turn setting got rid of the surge that's probably your problem. 5-6 turns is wrong.

The reason to get some kind of logger or tuning tool is that the BISS screw provides the basic idle air. When it's set correctly the ISC then has the range to handle fast idle in very cold weather so you don't stall on starting, the dashpot function when you take your foot off the pedal suddenly, 'idle up' for accessory loads. It is possible to tweak BISS watching how that other stuff behaves but it's just a lot quicker to know how many ISC steps you've got when the car is warmed up in normal weather without accessory loads. Steps too low = turn the BISS in 1/8 turn and test again ... etc.

In other words this is a basic engine adjustment issue -- not really 'tuning' as the word is mostly used here.

My thinking is also that turning the BISS in several turns was just a temporary "fix" that masks what's likely the real problem, which I'm guessing is either a dirty throttle or faulty ISC or FIAV, or a small leak somewhere. I'm going to remove everything and give it all a good cleaning, test the sensors, signals, vacuum, motors, BISS, etc., replace all the gaskets and o-rings and maybe some hoses, etc. Then I'll test it all again.

While I'm at it I'll probably remove and clean the plenum, fuel rail, injectors intake manifold and all the other fuel delivery components, since the whole system's never been overhauled and I was going to replace the filter anyway. The car sat for 5 or so years and while I got most of the old gas out some remained and could have gunked things up, and this will be a good opportunity to clean everything and replace what needs to be replaced.

I also plan to drop the tank and clean and coat that, and replace whatever hoses, lines, gaskets, strainer and such as needed. Basically I'm going to overhaul the entire fuel and air delivery system, and hopefully that gets everything back to nominal or as close as can be expected on a 30 year old car. While I'm at it I'll probably also remove the exhaust manifold and clean that and replace the gasket and mounting studs, washers and nuts, and maybe even take out the turbo and clean that up too. I mean might as well.

 

[steve]

I'm going to remove everything and give it all a good cleaning, test the sensors, signals, vacuum, motors, BISS, etc., replace all the gaskets and o-rings and maybe some hoses, etc. Then I'll test it all again.

Be careful not to remove the dark sealing compound used at the factory to fill the last few gaps around the butterfly and the throttle bore. You don't want the butterfly plate looking shiny to edges. You can clean up the bore but careful with solvents going into the FIAV. I don't know if they attack the o-rings or the substance that causes the FIAV to move.

Getting the ISC steps down (or up) to about 30 steps at warm idle is pretty important. Once you get the idle speed down to 750 or what ever you have programmed the ECU to is where the ISC steps will start to move.

 

[XC92]

Be careful not to remove the dark sealing compound used at the factory to fill the last few gaps around the butterfly and the throttle bore. You don't want the butterfly plate looking shiny to edges. You can clean up the bore but careful with solvents going into the FIAV. I don't know if they attack the o-rings or the substance that causes the FIAV to move.

Getting the ISC steps down (or up) to about 30 steps at warm idle is pretty important. Once you get the idle speed down to 750 or what ever you have programmed the ECU to is where the ISC steps will start to move.

I'm going to be super careful when I do this. I was going to do it pretty soon, after I order and receive the new gaskets, o-rings and other parts. But I decided to put it off until I'm ready to overhaul the rest of the air intake and fuel delivery system and have all the parts ready.

I'll probably work my way from back to front, first the tank, then the engine bay components. This way I won't have to worry about a dirty tank messing up my work up front. I want to be methodical about this, as always.