You need to do two things: fix all your vacuum leaks and make sure your ignition system is working properly. Then your IAC will be able to control your idle speed automatically.

Do an intake pressure test to fix your vacuum leaks. Also, wrap your BISS screw about 4X with teflon tape. That will seal it and keep it from falling out.

Next make sure your ignition timing is good. Then put your timing light on each plug wire. The ones that don't show up very strong on the ignition light have some sort of problem. Either fouled plugs, too high resistance in the wire, tear/crack in insulation or something else making the spark weak in that wire.

 

There is an idle speed adjustment screw. Its on the left side of the throttle body, kind of under mid level of where the Y-pipe pops onto the throttle body. Its a phillips head screw with a locking nut which you have to loosen first to turn it further in. Its actually what everybody should be adjusting assuming everything else is correct, such as no vacuum leaks, and a working and properly set TPS and ISC.

Sam

 

You need to do two things: fix all your vacuum leaks and make sure your ignition system is working properly. Then your IAC will be able to control your idle speed automatically.

Do an intake pressure test to fix your vacuum leaks. Also, wrap your BISS screw about 4X with teflon tape. That will seal it and keep it from falling out.

Next make sure your ignition timing is good. Then put your timing light on each plug wire. The ones that don't show up very strong on the ignition light have some sort of problem. Either fouled plugs, too high resistance in the wire, tear/crack in insulation or something else making the spark weak in that wire.

:stupid: VERY GOOD ADVICE

 

There is an idle speed adjustment screw. Its on the left side of the throttle body, kind of under mid level of where the Y-pipe pops onto the throttle body. Its a phillips head screw with a locking nut which you have to loosen first to turn it further in. Its actually what everybody should be adjusting assuming everything else is correct, such as no vacuum leaks, and a working and properly set TPS and ISC.

Sam

Would like to politely disagree....

What you are describing is the SAS (also erroneously referred to in some parts of the manual as idle adjustment) that should NEVER be used for adjusting idle. The SAS is set at the factory and should never need to be adjusted. (there is a procedure for checking/setting proper SAS in the fuel section of the manual.) Attempting to adjust idle speed with the SAS will likely open the TPS switch and the car will NEVER idle correctly.

ADJUSTMENT OF FIXED SAS
NOTE
(1) The fixed SAS has been factory-adjusted. Never
attempt to move it.
(2) Should it be out of proper adjustment, adjust by
following the procedure given below.
(1) Sufficiently slacken the accelerator cable.
(2) Loosen the lock nut on the fixed SAS.
(3) Sufficiently loosen the fixed SAS by turning it counterclockwise
to fully close the throttle valve.
(4) Tighten the fixed SAS slowly to find a point at which it
contacts the throttle lever (where the throttle valve starts
opening). From that point, tighten the fixed SAS further 1 l/4
turns.
(5) Holding the fixed SAS to prevent it from turning, tighten the
lock nut securely.
(6) Adjust the accelerator cable tension. (Refer to P.l4F-3.)
(7) Adjust the basic idle speed. (Refer to P.l4A-63.)
(8) Adjust the closed throttle position switch and throttle
position sensor (TPS). (Refer to P.l4A-65.)​

Proper idle requires:

1. Correct SAS adjustment (see manual for details)

2. Proper TPS adjustment to make sure idle switch closes (see manual for details)

3. Proper throttle cable adjustment - not too tight or TPS will not close correctly

4. Proper BISS adjustment to center control range of ISC (see manual for details)

5. Functioning ISC - Quick check is to turn steering wheel left/right. If idle speed does not increase there is likely a problem with the ISC. (although it could also be a defective power steering pressure switch)

UCSB VR4
Throttle body only provides air - has absolutely nothing to do with Air/Fuel mixture. ECU uses feedback from O2 sensors and air flow signal from MAS to determine proper amount of fuel.

What makes you think youa re running lean? Do you have an AF gage / wideband O2 or are you using a datalogger?)

FUEL MANUAL
Link to fuel manual PDF if you don't already have a manual. (service procedures start on page ~65)

http://www.ecanfix.com/users/manualcd/gift/3s/3s_fuel.pdf



Clint

 

Didn't he just say, adjusting the BISS wasn't helping? I thought I read that. Two Mitsu techs told me that we shouldn't be turning the BISS screw very much if at all from factory specs. Usually, the issue is unrelated to the TB, and the BISS is only there to compensate for clogging ports in the TB from age before it needs to be rebuilt or replaced or an aging ISC and/or deposits in the ISC port.
Clint, you act like I am talking out of my ass. I know these cars as well as you do and have been tuning mine and others since 99. I am not a newb and there are many ways to skin a cat. I just prefer the most direct route that isn't going to make your ISC max out or drop to nothing when the guy already said the BISS is not helping.
I just think if a person does not have proper knowledge of all the functions of the throttle body and the proper way of setting them, they should never attempt to touch it themselves.
The SAS can be adjusted and is the better alternative to fixing a low idle over the BISS adjustment assuming you have eliminated all the other causes for a low idle which may be caused by an improperly adjusted TPS, a malfunctioning ISC, poor charging or leaks either withing the TB mixing body, clogged bypass orifices, or a leaking BISS port.
You have disagreed with me in the past, and it doesn't bother me because I know what I am saying works and its been tested on many cars with satisfactory results. The manual is not incorrect. They just recommend you leave it at the factory setting, but wear of the SAS screw where it contacts the throttle linkage can and will drop your idle speed after a decade of use. If he is at 700rpm, a slight turn of the SAS screw and an appropriate adjustment of the TPS will fix the issue assuming he has no leaks.

PS---Many people should be replacing their throttle bodies after more then 100k miles on the clock, especially on a turbo car that has spit tons of oil and blowby through it. Wear on throttle shafts, leaking BISS port, hardened carbon deposits in the mixing body, worn throttle plates, all these things will make it go bad. You can rebuild it and replace the sensors or just replace it as an assembly like I did with mine. My car runs so much smoother with a new throttle body that I am pissed I even wasted the time cleaning and adjusting my old one.


Sam

 

Didn't he just say, adjusting the BISS wasn't helping? I thought I read that. Two Mitsu techs told me that we shouldn't be turning the BISS screw very much if at all from factory specs. Usually, the issue is unrelated to the TB, and the BISS is only there to compensate for clogging ports in the TB from age before it needs to be rebuilt or replaced.
Clint, you act like I am talking out of my ass. I know these cars as well as you do and have been tuning mine and others since 99. I am not a newb and there are many ways to skin a cat. I just prefer the most direct route that isn't going to make your ISC max out or drop to nothing when the guy already said the BISS is not helping.
I just think if a person does not have proper knowledge of all the functions of the throttle body and the proper way of setting them, they should never attempt to touch it themselves.
The SAS can be adjusted and is the better alternative to fixing a low idle over the BISS adjustment assuming you have eliminated all the other causes for a low idle which may be caused by an improperly adjusted TPS, a malfunctioning ISC, poor charging or leaks either withing the TB mixing body, clogged bypass orifices, or a leaking BISS port.
You have disagreed with me in the past, and it doesn't bother me because I know what I am saying works and its been tested on many cars with satisfactory results. The manual is not incorrect. They just recommend you leave it at the factory setting, but wear of the SAS screw where it contacts the throttle linkage can and will drop your idle speed after a decade of use. If he is at 700rpm, a slight turn of the SAS screw and an appropriate adjustment of the TPS will fix the issue assuming he has no leaks.

PS---Many people should be replacing their throttle bodies after more then 100k miles on the clock, especially on a turbo car that has spit tons of oil and blowby through it. Wear on throttle shafts, leaking BISS port, hardened carbon deposits in the mixing body, worn throttle plates, all these things will make it go bad. You can rebuild it and replace the sensors or just replace it as an assembly like I did with mine. My car runs so much smoother with a new throttle body that I am pissed I even wasted the time cleaning and adjusting my old one.


Sam

I was couteous/polite in my earlier post.... and will attempt to be civil.

What you are suggesting is contrare to the service manual references sited / posted earlier. factory service procedures do work.

183K on my odo. Original throttle body - no leaks - only replaced the BISS screw/o ring. Works fine.



Clint

 

the sas is only there to adjust the butter fly valve to that it does not bind against the bore of the throttle body when closed. It should not be used to adjust the air-flow into the engine. - That is what you are doing when you do the factory adjustment. back it out until fully closed - then run the screw back in 1.25 turns past touching. For all practial purposes it is considered closed.

Clint - I would bet your tb seals are leaking.

sam

 

My throttle body has 160k on it and I have replace Biss O ring and throttle body O-rings and it works great. Replacement of those parts cost less than 3 bucks. I wouldn't recomend a new throttle body unless there was a structural problem like a crack or something.

 

Again, you disagreed, but your solution was basically telling him to do exactly what he did already. My solution was direct, straight forward and its a viable method of setting your base idle---thats why its a threaded screw with a locknut, just like the BISS screw isn't a sealed port.
The factory service manual has suggestions and makes references to procedures that a technician can use to properly fix and diagnose issues with a relatively well maintained car within the typical lifespan of the parts involved. We shouldn't be turning the BISS more then a few degrees from factory to make small incremental adjustments. He even said he tried to turn the BISS and it was doing him no good. Thats the reason I suggested the SAS as an alternative to the BISS and you disagreed--- You politely disagreed, and I am equally politely saying that I am not incorrect, its just another way of achieving the same thing if you know what your doing and know what to adjust.
The factory manual says not to attempt to do any of the transmission repairs either, but thats because they feel the job is too complicated for a typical technician. I have adjusted the SAS and made the changes necessary and had positive-long term results with no downside like when you turn on the AC and the idle doesn't come down or when the car gets hot and the idle starts going up and down---all of which happen when you start screwing around with the BISS and start turning it alot to get your idle to change.

Sam

 

My throttle body has 160k on it and I have replace Biss O ring and throttle body O-rings and it works great. Replacement of those parts cost less than 3 bucks. I wouldn't recomend a new throttle body unless there was a structural problem like a crack or something.

My TB did not need any of those things at 120k miles, yet it wasn't working properly because of oil sludge blocking ports that were too difficult for me to clean out (i am guessing because I cleaned it, but the issue was still there). In addition, with a new ISC at $200, and a new TPS at $150, it made sense just to get a new one. I was geting a surging light throttle response and it was diagnosed by two Mitsu techs as a 'bad TB' Both the stock TPS and ISC passed tests as outlined in the manual, and replacing them anyway was silly when a new one was $550. Put the new one on and I never had to fool with it again.

Sam

 

I had ideling issues but it turned out to be vacume leaks. There were small boost leaks also in the TB but those were resolved with o-ring replacements. If your having idel problems you MUST do a pressure test and check for vacume and pressure leaks.

 

the sas is only there to adjust the butter fly valve to that it does not bind against the bore of the throttle body when closed. It should not be used to adjust the air-flow into the engine. - That is what you are doing when you do the factory adjustment. back it out until fully closed - then run the screw back in 1.25 turns past touching. For all practial purposes it is considered closed.

Clint - I would bet your tb seals are leaking.

sam

If you look inside the TB off the car, and adjust the SAS, you will see light shine through as soon as the SAS screw contacts the lever and you start to screw it in to factory specs. That means air is passing through. It is very slight, but its there and if you turn the SAS a fraction more, you can effectively up your idle another 50rpms which is all the poster needs to be in spec. You should not have to have your idle at 1000rpms unless you have cams, otherwise the car has issues. I would try and eliminate any maintenance type issues first before even touching it, but I had to adjust mine on my original TB and it worked out well for almost two years until I recently added all of the mods in my sig, and then the car just wouldn't cruise at low speed correctly or when it was cold so i replaced it and now it cruises like it was new.

Sam

 

but I NEED to get my idle up, right now it's at about 700rpm. The damn thing stalls sometimes when I take it out of gear and roll to a stop b/c the idle is set too low.

The idel is supposed to be closer to 1K when coasting in neutral. A lot of good advice was posted, but it's clear the low idel is the result of some other issue. What does the car idel at with the AC one? While at a stop, does the idel raise when you turn the steering wheel back and forth?

 

Thanks for all the info guys, i'll be sure to check this tonight after work and get back to you. The engine has about 40 K on it and there are no vaccum leaks. I do see the air/fuel mixture on my arm I gauge (and i have a datalogger)... you can tell when i open up the idle adjust screw, the mixture goes lean (due to more air w/ same amount of fuel)... I have the ARC II installed so I'm managing the fuel injection voltages myself and cannot turn any knobs up a notch to compensate (this makes the car run way to rich just by one click)... This is why i'm trying to resort to another method - like opening up the butterfly valve at idle.

 

Hey Sam,
The idle adjustment screw you are speaking of... i'm assuming this is a different screw from the one on top that i turn counterclockwise to insrease the idle (bleeds air in). I'm trying to find the screw you are talking about. Say i'm the y pipe looking directly into the throttle body so all i see is a circle with the butterfly valve inside of it, what side of the circle am i looking at? is it about 7-oclock or so? thanks again.

I'd like to confirm that when I turn the screw clockwise, i am actually opening the butterfly valve(increasing idle speed). is this correct? thank you again.

 

OKAY I did some test and the idle does not change when turning my steering wheel at idle, so that seems just fine.
When I turn the AC on, the idle immediately goes down about 200 to about 500rpm... then shoots back up to 8-900rpm just 2-3 seconds later and stays there at a constant. This is about 100-200rpm above what it constantly is when the AC is off, however I was under the impression this is normal when the AC is on? Let me know guys

 

OKAY I did some test and the idle does not change when turning my steering wheel at idle, so that seems just fine.
When I turn the AC on, the idle immediately goes down about 200 to about 500rpm... then shoots back up to 8-900rpm just 2-3 seconds later and stays there at a constant. This is about 100-200rpm above what it constantly is when the AC is off, however I was under the impression this is normal when the AC is on? Let me know guys

Idle speed should increase when you turn the steering wheel left/right. The fact that idle speed increases with AC on is a sign that the ISC is at least partially working.

If the car stalls less with AC on, this is a pretty classic stmptom of BISS self tightening. Try turning BISS 2 full revolutions counter clockwise. Idle speed may increase momentarily but should return to 700 RPM at warm idle with AC off.

Probably a good idea to pull the ISC and give it a good cleaning / test as per directions at www.stealth316.com (search for ISC)




Clint

 

the sas is only there to adjust the butter fly valve to that it does not bind against the bore of the throttle body when closed. It should not be used to adjust the air-flow into the engine. - That is what you are doing when you do the factory adjustment. back it out until fully closed - then run the screw back in 1.25 turns past touching. For all practial purposes it is considered closed.

Clint - I would bet your tb seals are leaking.

sam

I didn't notice any leaks when I was pressure testing ~1 year ago but it wouldn't hurt to check it again. Only takes a couple minutes with a glad bag.....

http://www.3si.org/forum/showthread.php?t=200417

 

Glad bag - I remeber that . Just looking when I replaced my around 115k. They where as hard as a rock - cracked and the seal material had transfered to the throttle shaft.

sam

I didn't notice any leaks when I was pressure testing ~1 year ago but it wouldn't hurt to check it again. Only takes a couple minutes with a glad bag.....

http://www.3si.org/forum/showthread.php?t=200417

 

Hey Sam,
The idle adjustment screw you are speaking of... i'm assuming this is a different screw from the one on top that i turn counterclockwise to insrease the idle (bleeds air in). I'm trying to find the screw you are talking about. Say i'm the y pipe looking directly into the throttle body so all i see is a circle with the butterfly valve inside of it, what side of the circle am i looking at? is it about 7-oclock or so? thanks again.

I'd like to confirm that when I turn the screw clockwise, i am actually opening the butterfly valve(increasing idle speed). is this correct? thank you again.

If you do this and the TPS switch opens, it will never idle correctly (and you may end up replacing your TB in frustration) Adjusting the SAS is as crude as using the throttle cable to adjust idle speed. (It works but so does putting oatmeal into a transmission to make it quieter.)

As per earlier posts:

1. Idle speed is under control of the ECU / ISC

2. No reason to raise idle speed and if you attempt to raise idle speed outside control range of ECU/ISC, the idle will not be stable

3. Idle speed has absolutely nothing to do with running lean. If it is lean and O2 sensors are not cycling at idle, you likely have an intake leak.


Clint

 

Glad bag - I remeber that . Just looking when I replaced my around 115k. They where as hard as a rock - cracked and the seal material had transfered to the throttle shaft.

sam

Do you have a link to procedure for replacing / source of TB seals?


Clint

 

http://www.3si.org/forum/showthread.php?t=240262&highlight=throttle

I used the #7 o-rings.

 

Thanks for all the info guys, i'll be sure to check this tonight after work and get back to you. The engine has about 40 K on it and there are no vaccum leaks. I do see the air/fuel mixture on my arm I gauge (and i have a datalogger)... you can tell when i open up the idle adjust screw, the mixture goes lean (due to more air w/ same amount of fuel)... I have the ARC II installed so I'm managing the fuel injection voltages myself and cannot turn any knobs up a notch to compensate (this makes the car run way to rich just by one click)... This is why i'm trying to resort to another method - like opening up the butterfly valve at idle.

Ah, didn't know you had an ARC... Your tune might be the issue then. On my car, I had the same issue with idel (One click too rich, another too lean) when 1st installed the ARC. Tested for vac leaks (there were none).

What I ended up doing was getting a rich tune with the accell knob, then backing out the idel screw a couple turns till the 02s cycled. In this case, I was using the BISS to tune the A/F mixure. The idel imediately jumped to 750 and the ECU seemed happy with it (fuel trims weren't maxed).

Give it a shot.

 

Thanks for all the info guys, i'll be sure to check this tonight after work and get back to you. The engine has about 40 K on it and there are no vaccum leaks. I do see the air/fuel mixture on my arm I gauge (and i have a datalogger)... you can tell when i open up the idle adjust screw, the mixture goes lean (due to more air w/ same amount of fuel)... I have the ARC II installed so I'm managing the fuel injection voltages myself and cannot turn any knobs up a notch to compensate (this makes the car run way to rich just by one click)... This is why i'm trying to resort to another method - like opening up the butterfly valve at idle.

When ECU sees increased airflow, it will add more fuel - ECU also uses O2 to determine proper air/fuel mixture within limits based on current air-flow.

Take a look at O2 trim to see if the ECU is bumping up against high/low limits.


Clint

 

Ah, didn't know you had an ARC... Your tune might be the issue then. On my car, I had the same issue with idel (One click too rich, another too lean) when 1st installed the ARC. Tested for vac leaks (there were none).

What I ended up doing was getting a rich tune with the accell knob, then backing out the idel screw a couple turns till the 02s cycled. In this case, I was using the BISS to tune the A/F mixure. The idel imediately jumped to 750 and the ECU seemed happy with it (fuel trims weren't maxed).

Give it a shot.

This is a great suggestion but when I try this the car idles like shit (granted the rpm's are higher). It constantly hesitates and the rpm's shoot down everytime arm is on the low side of stoic equilibrium and then recover on the rich side of stoic. Also I can hear a huge air rushing noise under the engine bay like a vac leak (after all isn't this creating a vac leak when you back the screw out? doesn't it just bleed air in from atmosphere?) - aside from this i really don't want to turn anymore fuel knobs up as the car is already running rich overall (this just worsens the richness of my settings).

when I have the screw tightened all the way down the thing idles like a champ at a stop, but when I shift into neutral... rarely the car stalls - and we all know rarely is WAY too often to have a car stall when your in neutral coming to a stop and don't want to lose your steering and braking capabilities.

I've decided the best solution to my problem is by increasing the idle? anyone have a better suggestion that will allow me to keep the idle adjust screw tightened down?