The ISC , Idle Speed Control valve 91'+  in the USA !                                        
Located on right side of G16a throttle body 8valve (TB) or on left side of huge plenum box Intake manifold) of the G16B MPI 16v engine.
Fast facts:  1989/90' facts are here>>>
The car  owner or mechanic never sets idle speeds, the ECU is hard coded to 800 RPM hot. The ECU forms a closed loop servo action, at hot idle using the above valve.  You can only set
the DUTY cycle to 50% hot.
Suzuki changed the name 3 times. (maybe 4)   I  call  it  the ISC,  the IAC is thermal only device below the TB. It has no wax thermosatic valve action like the IAC..
This is just an  electromagnet air valve solenoid, that runs on 12-15vdc (battery / alternator voltage)
The 2 pins are just a coil of wire, (copper) forming what is called the classic electromagnet (study
Maxwell?). The coil is 12 ohm  (6 ohms  year 89/90').
The coil is modulated 200 times a second, called 200Hz, and is also called PWM modulation. (the period is .005 seconds, 
the DUTY cycle to 50% hot. per the shop manual)
The connector wires are blue-black is +12vdc power.  The ECU grounds (-) the other green wire. (with a square wave, grounding transistor)
The valve is 100% closed with 0v power, or unplugged. (and open fully with 12vdc applied)
Apply 12vdc to the coil (unplugged !) and it opens, do so for only 1second at a time. or it will over heat manually powered up with test battery.
The valve usually never dies 100%death, it usually just gets dirty, so clean it with MAF  cleaner (safe for plastics)
The valves rubber  seat ,after 20  years of 1 trillion cycles  it looks like a  prize fighters mug, all beat up. (and leaks) If it leaks too much I recalibrate it.
 

Idle speed control,  see my manual in hand test ,  1991+ ISC test video here. (clean it first)
The coolant lines are used to heat the whole Throttle body starting in 1991. 
The 1989/90 has no water or air  hoses (above) or nipples (above).  The newer valve above, is much easier to test.1991+
The ISC can go out of control with massive air leaks (vacuum leaks)
The ISC  Air tube?, if you pinch it on a HOT ENGINE that tube hose,  , the idle will drop ot about 400 rpm (from 800) and nearly stall.,) (the 400 is on normal running engine)
If the RPM is too high now pinched,  say 700 rpm you have and air leak not caused by the ISC,!
I turn the air bleed on the trottle body CW full now,  and pinch this hose, if the enigne does not stall now, you have gross vacuum leaks somewhere ,unrelated to ISC.
That 400 is not in any books, it empirically derived. (by me) {trail and error}  See how to test the ISC here. See up to 50 tests for out of control fast idle here.
That 400  RPM allows the ISC to open 1/2 way and hit 800 rpm easy.
If you have bad air leaks,(vacuum) the ISC can never close more than 100% and hit 800 RPM hot.  (800 means 750-850 RPM spec) Hot all accessories off. (then turn them on and it holds 800)


PURPOSE:
The purpose of this device is to regulate idle at 800 rpm HOT (even in DRIVE with an A/T) and to raise idle to 1000 RPM with A/C  on, or P/S overload (on 89/90 Headlamps on)
My Manual tranny car drives easy with a bad ISC, but you A/T owners , no way Jose'  , your car will stall ! 

The A/T cars will hold 800 RPM in DRIVE. if it stalls the ISC is dead or engine power is super weak.

I have cleaned many by filling it with MAF cleaner and stroking the plunger with a split Popsicle stick or tooth pick.  (block the air tube on top , invert and fill the side port with cleaner)
Failure modes,:
1: Dirty and stuck  (oh, so common) stuck open or close or just stuck period.
2: Coil burned open  not 12ohms. but infinity bad.
3: Will not open , 12vdc applied (1 amp min. source of power (battery or power pack 12vdc.) Blue/black wire is PLUS pin,
4: Will not close,  stuck open or the set leaks.. 
5: makes too much noise , at idle (89/90 like to do that)  RATTLES like mad deal.

Manual testing with a power supply or 12v battery:

Warning , only apply voltage to the ISC (testing ) for no more than 1 second in 10 seconds, to prevent overheating coil. (90 FSM warning)
Let the coil cool off after powering it up.  It can do 10 one second hits. then I  rest for 1 full minute.

1991 to 1995 shown:  ( 8v and 16v are near identical looking and in fuction but nipples rotated uniquely)



TB = Throttle Body  ,   I like using "TB"

It is just a solenoid air valve,  it flutters at 200 times a second or more, and is 100% controlled by the ECU.
 (PWM ,pulse width modulated , but is also modulated by the ECU with a hot engine, to hold idle at 800 RPM under all   idling conditions and loads from Head lamps ,dash blower fan and Park to Drive selections)
It can malfunction in many ways.
It has other functions running besides just idle control , it controls Deceleration air bleed (and reduces pumping losses while driving., neck snap reduction)
This device failing, can cause other  DTC's to fail.
You need to understand there are 2, AIR IDLE valves on this car,  this one above, and the IAC purely thermal version, located on the bottom of the TB:


The coil can open , short or ground out. or the internal plunger can seize.
The internal piston can wear out and just rattle, continuously to the sympathy of the air induction vacuum pulsations. ( see a lots of 89's do that)
The normal coil resistance is (Suz spec.)11-14 ohms at 68deg temp.  Use the OHMS  Rx1, test section of your DVM.  (DMM, etc) to measure this internal coil.
Always measure the coil resistance , first thing.   (must not be  0 ohms, and not infinity)  12.3 Ohms would be a good reading. Like mine.
The 89/90 ISC coil is 1/2 this amount at 6 ohms, so don't be alarmed with early ISC coils being low.  (so never use a 89/90 TB on any 91 and newer car and ECU)
I blow air in the air nibble with a clean hose  (on car or off car) with lips. I blow, it must not leak air. (most will).
If it leaks too much air , I recalibrate mine..  (after cleaning fully and the piston inside is fully free)
On car checks,  the keys in pocket, blow in air hose with lips test, must not leak air.
On car, I do the the DUTY cycle to 50% hot. and that fails, I can not attain 50% duty cycle. per the FSM pages.
On car (keys in pocket again) I can apply 12vdc to the coil  Plus to blue wire. The valve opens and I can now blow, in the air hose per 2 lines up.
On car I can measure the coil opens.
On car I see if the idle switch is closed at 0v, and if not, its 5v, then the ISC is shut down by the ECU, on purpose.  (that needs to be calibated first and next  called TPS calibration)
I can load test the ISC on car. running, I see 800 RPM hot, I turn on all electrical accessories, not A/C and RPM holds at 800 RPM, I can now select DRIVE, (shifter) and RPM holds at 800, this proves ISC regulation is working.
Off car, tests, I can blow test it with my lips , 0v and 12v appled.
Check the coil ohms off car.
I can clean it off car.
For more details of these checks and even calibration see the below.


TESTS:     OLD TBI system has no coolant hose and is missing the fresh air hose, making it harder to test.  23 years old (and counting)


The NAKED EARLY ISC:
I will show how to check,  each generation of Sidekick (Tracker);  89'/90' and 91'+
First the 89-90's: a 6 ohm coil !
This ISC device in these 2 years only, loves to go bad and rattle, some ignore it others fix it.  It's your call,  It might rattle and work pretty good.
These 2 years are unique, they do not have 2 water hoses, nor  the 1 air hose. ( sadly, for easier testing. )
Not only that , if you unplug its connector the motor dies. , due to that connector sharing the injector power. (IIRC)
I cut the wire to the ISC to see if RPM  drops to about 400 RPM and it stops rattling if in fact it does.  
The 89/90 car has no idle air bleed screw in the TB, like all other years  91-98, have ! But these 2 years, the idle stop screw sets hot RPM to 800.
You can not attain 800 hot.  block the ISC ports.! 
The below, are the only tests you can do on  an  89/90 ISC ,
Remove it, clean it. (carb cleaner works great, as does throttle body cleaner). The Best cleaner is CRC MAF cleaner , safe for plastics...
All electrical Accessories are off,  ALL !
  1. Make sure the ISC internal port blocks air , with no power applied.  (your lips blowing on 1 hole only) use a rubber tube , ok?
  2. Make sure it opens fully, when power IS applied (12vdc battery)  (blow again)  use a clean rubber tube to keep lips clean.
  3. Make sure it doesn't rattle. (shake it , this is a common fail after 20 years)
  4. Make sure the ISC coil is not open.  (nor shorted to ground, all years) Either conn. terminal to ground must read infinity ohms.  6 ohms is spec. IIRC
  5. You could  leave it removed whole ISC from TB and start motor HOT,with the two holes above open (causes huge air leak)
  6. These open  holes now, the  motor will race really fast. (I'm not sure how high,  I guess at 1200 RPM hot. be ready at the key.) It will scream. for sure.
  7. The dashpot must be retracted, at all tests. If not all this is just a waste of time...
  8. I then block, both holes with duct tape.  Now you have zero flow of air from the ISC function.  RPM's  must drop to near 400 RPM.
  9. If the RPM does not drop, there are huge air leaks, in the plenum system (induction it's called)
Too Fast idle, is NO proof of a bad ISC, most fast idles, are caused by other problems, air leaks, advanced ignition timing, bad thermal IAC?

Run the engine, and see if idle drops to 400-500 rpm , if not , you have massive air leak in to the plenum. Hint:. fix that first.
Watch out, the 89/90 can raise idle 5 ways ( in theory )  All Accessories OFF.
  1. Head lamps on.  (not true 91+)
  2. Fan on  (not true 91+)
  3. Electric heater defrost on. (not true 91+)
  4. P/S overload (ever hear your Power steering squeal when over cranked.  bingo overload. (all cars)
  5. A/C on.  some cars have A/C as an option. (all cars)
The 89/90 has a 3 way diode block that  allows the first 3 to happen above.
The ECU pin must be at 0v volts out of the diode block or you get fast idle mode. 12v causes a fast idle.
The P/S pin is Ground true, if the wire grounds out , fast idle
The A/C pin , is 12vdc true.  ,if the switch is present and outputs 12v, you get a fast idle, even if the A/C compressor removed (gone)


1991 to 1998 ISC TESTS:
OFF CAR TESTS:
You can remove the ISC ( some fluid loss results) ;  Test it on a bench with a 12vdc battery or use car battery. Any 12v battery will work.1.0amp source.
You can also apply 12vdc to the pins and hear and see  it click/ operate.
 ( if it don't click and move , then it is bad)    
 See my MY FLASH Video !: doing the off car test 91-98 ISC.

Off car you can blow into the top tube, and it must  block air flow.  98% , it never blocks 100% oddly we are told (new parts tested by friends)T
then off car apply 12vdc to the connector and the valve opens and allows you to blow air into the top nipple.
It works just like a lawn sprinkler valve , only it uses air not water.  Not a big deal.

ON CAR TEST:
Start motor. HOT !
With connector PULLED, the  valve is closed and the motor will nearly stall (my 96' stalls) on some 8v motors idle goes really very low. 300-400rpm..
(if you apply 12v  to the connector,  on car and a running motor, it  will race at a very high rpm.) (all tubes connected !!!)
My 1996 KICK , when I pinch the top air hose (rubber) the motor almost stalls (hot). so it is the major contributor to air , besides the air bleed.


More, On car tests:
There are 2 tests, 
Start motor.
On the 8v you can pull the air tube and fell the modulation of the air being sucked in , and then plug the tube and the motor will drop RPM drastically.
The 16v do not pull this hose as it creates illegal air. (only pinch this hose on a 16v motor for testing)
8V;  air tube removed:
If no air flows at all, the valve is stuck shut.
If air does flow, then pulling the electrical connector should stop the air flow, and cause Idle to drop quite a bit. (below 800 RPM hot) Most car go below 500rpm.
If it is not pulsing this air flow , then the ECU might not be doing its IDLE process, or ISC is clogged , stuck, gunked up.
The 16v you can pinch the air tube and see RPM drop , and then unpinch it and then pull the connector and RPM should drop again.



Advanced users: the DUTY cycle to 50% hot.
Putting a DSO or  scope across  the 2 pins (back probing and engine running) you can see the modulation. (DSO is digital Storage O-scope)
70 to 200 pulses per second are typical. (less on early models)
You can see the dutycycle changse as you turn on HeadLights and heater fan. 20amps flowing will cause idle to drop and ECU will command the ISC open more.
If the duty cycle changes and the ISC does not react (track dutycyle) then the ISC is dead.

Calibrating Idle and Duty cycle is covered here:


This actuator plunger inside, can clog and can be cleaned with Carb cleaner.
The thermal portion of this 91+ valve ,  only warms the Throttle body , the ISC does not change with heat.  (this l IAC under TB does the thermal changes to idle)
I dismantled one, to learn that.


LIVE TESTS:  (FSM test)  ( all tests above pass)  ISC installed properly.
Valve is passing tests above.
One can do a full test of the electric portion, by placing loads on the engine and then see that the idle stays the same.
Air conditioning on moves the idle (HOT) to 1000 rpm via this device. ( assumes the normal 800 rpm has been set correctly).
Head lights on, and the idle holds at 800 , the same with the Defroster, the cab fan and the automatic going into Drive , 1 ,2  gears.

That is the purpose of the electric portion and that is to hold the idle to factory specifications, under any load.
This valve is also used while driving, and not at idle ( during fuel cut and EGR tests, and to reduce pumping losses, and economy )

Make sure this device is mounted solidly and the gasket is not cracked, if loose, it will allow illegal air to enter the engine.


The factory idle calibration , also effects the operation of this device.

In fact, the setting of the idle , will fail if this device is defective or clogged with PCV/ EGR generated  sludge.


Last and not least, an off car test and calibration of the ISC an 8 valve unit shown here.  ( exact methods 8v , detailed)
  1. Remove  (ISC)  from the throttle body.  
  2. Check coil for 11-14 ohms, (mine reads 16 and is ok) using a simple ohm meter.  (6 ohms for 89/90)
  3. With a small   screwdriver (1/8 blade slotted) or a popsicle stick is better,  try to move the plunger inside the TB side port.
  4. The plunger must move about 1/8 of an inch, if it does not , it is seized and you can try cleaning it with carb cleaner then lubed with silicon oil spray.
  5. Watch the video. !
  6. Apply 12vdc power supply to the coil terminals, the plunger must move 1/8 th of an inch, or  3mm.    ( power source must be capable 2 amp current)
  7. If the plunger  is free, then blow into the Air tube and see if the application of power can make the valve open and close.  power applied opens the valve..
  8. Do not adjust the  hex socket screw on the end  of the ISC. but I did one time on my 91 due to the seat (rubber) was worn and leaking.
  9. If the plunger is free, one can adjust the balance, with the  hex Allen screw so the valve just closes (there are 2 springs inside the unit)  <last resort here... ok?
  10. While looking at the plunger, through the port opening, turn the screw plug CW until you feel a restriction while blowing on the air tube.
  11. Then when I apply power to the connector , the air flow will be not flow  98% closed, until I apply the power. By default the valve is closed.
  12. 12 vdc , valve open,  0 vdc , valve closed.  The valve does leak a tad when closed, that is ok.  (new valves, do leak closed)
If you can get this far, the valve is good and can be put back into service.
I never attempt to adjust mine "ISC", unless it is clean and motor runs perfect andI can not get the TB main, idle bleed down to 800 rpm.  (a $300 part, so ....)

With the car running I can feel the valve plunger, wiggling like bees wings.  ( by touching my screwdriver to the plunger and my ear. buzzzzzzzz ).
I had the TB port hole blocked with ear plugs. ( doing this step on a 16v may be possible  with duct tape tape or corks, to seal it up ?)


Seeing it work, is everything, right ?

91-98'    (this is HACKING , to save $200) If it leaks air, you have nothing to lose. at he 5mm Allen hex screw.
Do a 8Valve ISC, recalibrate , because you found the seat worn and the valve leaking , deEnergized.  (FSM says replace it )
Adjust the factory set, hex screw, so the valve plunger tip , just barely touches (kissing) the seat.   ( this is a last hope solution, as the valve rubber seat  is torn up...as every one I've see is)
If the idle is too low, then adjust the ThrottleBODY air bleed screw (rubber plug hides it) for more air CCW and proper idle. The correct way is to set RPM isduty
Bleed screw, is located on the Top of the  TB 16v ,  front of TB 8v  and never to be found on 89/90 Kicks.
The 89/90 has no  bleed screw, the  hot idle set, and is the throttle butterfly stop screw sets duty only these 2 years., do no touch this screw starting in year 1991, (usa)
The kissing point will still leak air but only a very little amount (using lips at the nipple)

But never play with the throttle butterfly stop screw on any car 1991' or newer, it is factory set and adjusting it will be very bad news. See the real "FSM"

Key points !
The ISC , ECU controls are dropped, if the ECU enters LIMPHOME mode. (or worse, backup mode).

Always set idle last.  Always troubleshoot all other running problems first, then set idle.
 This List below shows my , to be corrected FIRST !  ALL May cause the ISC fail. !

  • Timing not advanced or retarded (IGN)  
  • EGR not stuck open
  • Vacuum solid at about 19 inches HG, ,at idle and NOT PULSING !  (HG = mercury column in inches, HG = latin atomic symbol for mercury)
  • Cam belt not slipped.  ( timed perfectly !) The cam must be timed !
  • Motor tuned up , a full tune up with filters.
  • Injectors not leaking, when deEnergized.
  • Check engine lamp off and codes reading 12 code DTC. (normal)
  • Not in Limphome. (failsafe/backup, Suzuki calls it )
  • No ILLEGAL air leaks to the Plenum. (induction system)    bad vacuum hoses, induction gaskets cracked.
  • Fuel pressure not above 39.8 (8v) and 42.7 PSI (16v) static.  Pump will exceed 60 psi ,dead head.
  • TPS must signal idle (the idle switch ) or no Idle regulation will ever happen.
  • The A/C and all electric loads need to be off or the idle will not be 800 but will be near 1000 rpm.
  • The PRND switch in the side of the tranny must signal not Park or neutral driving or the idle will fail at traffic stops and engine will stall.
  • The engine must not be running grossly rich or lean.  Fueling issues.
  • The Power steering over load switch can cause 1000 rpm.  if it fails.
  • A weak MAF or MAP can cause ECU  to loose control of idle.
I can not over state this,  DO NOT SET idle or expect idle to work on a sick motor , or EFI system. .  
Go ahead and try, but it may  not regulate.   Espcially on , a  very lean running engine.
This valve only regulates idle, only you can set the regulation point ,only by adjusting the Throttle body  BLEED screw. To 800  RPM

If battery voltage drops too far the ISC may malfunction,  so will the ECU.  10 to 15vdc is the normal range of voltage at the battery.
Running is near 14.5v (13.3 to 14.8 depending on battery charge states)
Key on no start ,is 12.6v.

Hot engine illegal air  leaks:  BAD VACUUM leaks.
Vacuum leaks have many paths to the induction plenum. (below the throttle plate is  this plenum area , at 20" vacuum HG)
There are 2 states of being here,  the ISC regulating and not.
If the ISC is not regulating we can find all air leaks easy by pinching  all hoses , see RPM drop and bingo that hose is leaking for sure, or its end of hose device leaking air (a vacuum leak) (the ISC hose always leaks so this drop is normal)
If the ISC is regulating , hose pinches are hidden, by the job 1 of the ISC as it regulates and hides  the leak you just found, or failed to notice.
To solve this riddle we need to defeat the ISC, unplug it and turn the bleed screw out, so engine can run.(with no ISC) (tricky, but can work if the leak is huge)
Better? sure !
Or use the DUTY meter,  and if say duty now is 65%?   and you pinch all hoses (not the ISC hose) say you pinch the VSV evap hose and DUTY cycle  DROPS fast, this is a leak in this line.
See what I did there,  I used the meter to find all leaks on all vacuum lines.
My pinch page is here.





Ver 7 - 6-15-11  ,

  Jargon got you perplexed?, see this. (top  of page)



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