89/90 sidekick idle speeds 800/920rpm

[spiritofr]

Hi all,

I have an 89 Sidekick JX 2-door 1.6L 8V TBI, and as I understand there are 2 normal hot idle speeds: 800rpm with nothing on, and 920rpm with headlights, fan, etc. on. I'm experiencing a small abnormality that I was hoping you could help me with: my car hot idles normally at 800rpm, and when the fan or parking lights are on, it goes to 920rpm like it should. However, when I switch from the parking lights to the main headlights, the idle drops to about 850 or so. When I switch it back to just parking lights, it goes back to 920, then back down to 800 with all lights off. What do you think could be happening? I'm guessing the CPU isn't recognizing the headlights being on so it's not initiating the fast 920 idle, and I guess the load itself is causing the normal 800 idle to rise to 850... Any input on what could be the issue and how to fix it would be greatly appreciated.

Thank you for your time and help!

[fixkick]

no transmission stated or ecu part number, some cars have the wrong ecu. like my m/t had a A/T ecu. and can be tricky doing that.

yes the ECU has only one idle up pin, and a diode "or tied logic" to get more idle up inputs.
sounds like the head lamps overload the alternator ,or the ISC is messing up some way. (duty cycle not at 50 % or on the cusp of failing?)
your tachometer is very good to resolve, 50 rpm, .

lets look at that.
the wiring is very very simple. for idle up.
best is this page set... the diode block is on page 2.
the red-yellow wire (park/tail) is hot, in park and also low beams.
so is at 12v, with head lights on, (it should be, or you'd notice)
id say the ISC is overloaded by the HL. (straw that broke camels back deal, or more exactly the ISC cant open more.)
so take the idles stop, hot engine 800 rpm and open it a touch more . and now the iSC has more freeboard )
or set duty to 50% by getting DC volts on ISC pins near 7v hot idle. (1/2 x 14v)

http://www.fixkick.com/ECU/89/1990-scan-...lpages.pdf

off my bad idle 89 page.
The ECU went nuts and ISC with it? Bad inputs to the ECU can cause that:
The critical pins on the 89/90 -60Axx ECU are:
FAST IDLE COMMAND PINS: A= Y B = G , Suzuki to GM pin number changes, colors never change.
A3 = 0vdc fast idle from diode module, (fan,defrost,headlights are on, any or all)
A2 = 0v, A/C is on,
A13= 12v , if 0v your P/S is in overloaded ,fast idle feature.
A14 = 0v the TPS idle switch, if not 0 then TPS is signalling off idle ,bad TPS or maladjusted.
B12, 0v , A/T PRN switch sigs. only this signals I'm in drive if not 0v. 0 means park or neutral. This pin if at 12v, cause ecu to NUTS in PARK or Neutral, for sure. (m/T cars this is not used or 0v)
B11, 0v , of not at zero the ecu thinks you are cranking endlessly. that be real bad.

[spiritofr]

Thanks for all your help, my car is M/T. I will try to follow your advice step by step.

[fixkick]

i think the ISC needs calibration, i bet the 12vdc is on that diode pin, with head lights on.
so that means the alternator load , (120 watts added to it) slowed the engine too much , too much for the ISC to handle.
that if true , means the duty cycle is way off.
in fact just take the throttle stop screw and turn it say 1/4 turn clock wise opening the TV just a tad more. letting in tad more air.
it also means the ISC lost control of idle with head lights on.
if you have A/C i bet it does same.. my guess you dont have that.
and same with rear defrost heater wire';s missing or not installed but if still works i bet it can handle idle with that on either.

keep in mind the 800 and 920 rpm are all ECU controlled (hard coded) using the ISC as the control device.

---

setting duty cycle can be real easy to real hard.
depends on what meter you have.
if lucky the 7vdc trick works, (If the meter show 0 or say 14.7vdc this meter will not work) on 20vdc range. DMM meter.
and buying a duty meter is too expensive.

---

the signal is 200 hz square wave, and good meters on DC can average this out. to 7v at 50% of alternator output it will be.
with hot idle, (accessories off) see the throttle stop to 7vdc and bingo, 50%

this working allows the ISC (ecu) to add 50% air or subtract 50% air , it its will. so all electrical loads work.
worst case is A/T cars. shifting from park to drive.

[fixkick]

most shops do not know how to do this.
for many reasons.
1: they never seen old cars ever. (nor learned in school)
2: the newer cars , all this is removed, ISC calibration, is fixed now. we have bleed screws from 91 to 98.
so its something you need to learn to do DIY. as most shops would throw parts at it. (at huge costs)
3: the books show using a suzuki meter (duty) that is no longer made./sold or found anywhere..... most were just worn out and dead now.

3b: or a scope. (the most easy of all, and never ever fails to work, see the real thing) a real shop with no scope will never survive.
turn TV screw until the wave form is symmetrical.
3c: or a custom duty meter $$$$ turn screw for 50%
3d: some DMM's can do this, some have a duty meter mode. or the DMM 20vdc range works?,. (try it?)
if the meter 20vdc works, turn the screw until you see 7vdc. (back probing the ISC pins. using needle probes.)


so given all those facts. just try step 1. it's harmless, you can turn it back.. later if need be.. so.... count your turns.
just turn the screw TV stop 89/90 1/4 turn clock wise, adding air (in 91 + cars we open the bleed screw CCW) both ways add air.
what we are doing is centering the command authority of the ISC (new car verbiage ) going to 50% is best.

id do that lacking a duty meter, or try the 20vdc test.


what is happening on your car,is the ISC can not add 120watts of air. needed to run the alternator.
see?
so add some air, and if your added air , works that means your added air was added to the ISC and now it can work with HL on.
total air = ISC + TV air. it's just air, the ECU does fuel like magic.
simple algebra.. if the ISC runs out of steam(air) , add some air.
then the ISC can reach 920 RPM it the regulates there. your's cant reach there.

does that help...
think of a water tank that has 2 hoses.
one add water
and the second drains water
and you are the computer, that yells at the 2 persons on the 2 hoses.
the first hose is draining water this is the ALternator hose.. if you will
then the other hose is the ISC hose. water
the ecu sees the alternator suck out too much water.
so the ECU adds water. but the hose is too small. and fails. hummmmmmm

what to do? so you add one more hose, for adding water (the TV) and adds some with that,
now the ISC hose can do its job, which is keep the water tank 1/2 full at all times...
does that help>? the visuals.????

[spiritofr]

Thank you fixkick, this is great information, the visuals are extremely helpful! Is the TV stop screw the same as the idle adjustment screw, i.e. the one sticking out diagonally next to the dashpot on the back of the TB? Is there any other screw that I can turn to adjust idle on the TB? I thought this screw should never be touched on 91+? (I have an 89 but I'm just wondering because you said for 91+ it's CCW to add air...). When I got my car back from the shop a few weeks ago the hot idle was at 600 and the accelerator pedal was getting stuck sometimes (i.e. the butterfly valve was closing too tight and getting stuck) so I turned this screw clockwise 1/4 but it didn't change the idle, so I turned it another 1/4 and the idle still didn't change so I turned it like a full 1.5 turns or so, and it finally raised the idle to 800 but now the idle seems weird, it only gets to 800 after like 30 minutes of driving, as if it's taking forever to warm up or something... after warming up it stays at 1000 for half an hour of driving before it finally drops to 800... any thoughts?

[fixkick]

it is this screw. at end. of this post

your car is 90, not 91. the 91 has a bleed screw up top. added in 1991.... and very different procedures.
http://www.fixkick.com/IDLE-AIR/89-90-idle-air.html
the top screw is Dash pot screw, that one is never changed,but the calibration is in the FSM... ask, if need it.
the lowest screw, is the TV stop screw. (can be seen to move if you watch the tv) see photo below.
the TV stop screw, opens the TV as you turn the screw in, Clock wise. (right hand tread rules)

in 1991+ the valve is always closed at idle. and the bleed screw adds air, by turning it CCW, (opposite of 89/90) (like a water faucet does)

the reason they did this is easy, the 89/90 everytime you mess with idle stop. you destroy the idle switch calibration. (a royal pain this is)
so Suzuki added the bleed, makes that hassle no longer true.... they mention this in the 91 fsm.


that is correct.
if you turn the TV screw, and the idle doesn't change that means the ISC Servo regulation is working,! as you turn the screw in, and add air the ECU sees you do that, and closes the ISC , negating your fiddling...."seem like nothing changed" is correct action hot. !

600 rpm is Usually the EGR stuck open but if the TV stop screw is closed and the idle switch stuck open the ISC is dead and 600 is possible.

never adjust the TV on a cold engine. that is because the ISC is dead then, the IAC is open below 150F. (the duty cycle is set only HOT)

the idle speeds are all for a hot engine. cold is a totally other ball of wax. (Dash pot, on , then off, the IAC runs most of the air supply cold)

when the head lights were on hot, the idle. was too low. (implies ISC is out of steam) so open the TV a tad, CW on the screw, does the ISC wake up? hot? now?
I suspect your ISC is set to a way high duty cycle. (open too long) and when you selected HL, it could not open more. or enough.
and go to 920 like it does in park?
to correct just that, on a hot engine, with HL on, add more air, by turning the TV stop crew CW. this adds air and the ISC will suddenly wake up
an idle goes to 920 to 950 rpm. from 800 or 850. see?

lets do the whole ball of wax.
1: start engine, Dash pot is extended for 5 to 30second (temp. based) and the sucks back via VSV actions.
2: then the IAC IS THE predominant air supply causing 1200 rpm or more. Temperature dependent.... until 150F (yes the water pipes here must not be clogged)
3: the engine warms (thermostat not bad) and as it crosses 150F the IAC closes (IAC is in the base of the TB) if not?, engine screams like a banshee for ever...
4: engine is now hot. the ISC starts regulating all hot idle speeds, if the TPS idle switch is closed. (calibrated)
5: 800 hot, electrics off, and 920 with any of the IDLE up things a active (HL or park,defrost, blower,p/s overload/ AC ,etc.)

ok so they set your TV wrong, it is never allowed to stick ever, if it did the mech is not aware of how this TBI system works.
lets say the IAC leaks. hot.
so the mech, then closes the TV to correct that leak (bad idea that) now you risk having a sticky throttle (danger of getting rear ended for sure) or?
a dead wrong action.,
there are 3 phases. if step 2 fails, above, all bets off.

the procedure for the idle switch is hard.

if you adjust the TV the idle switch can do 2 things, wrong.
A: fail to close, and ISC is now dead. (unregulated idle)
B: if it stays closed too long the ISC is active as you step on the throttle and it fights you.. (acts very strange. like a hesitation but is not what many think is cuase)

That is why the 89/90 idle setting is so hard, with that screw.
setting duty cycle is no easy.

the cheater duty cycle is here. (no correct tools)
http://www.fixkick.com/IDLE-AIR/89-90-id...s_end-duty

the tps calibration is hard, or impossible if there are idle speed devices , malfunctioning....

http://www.fixkick.com/All-Pdfs/M89/TPS/...ation.html

the 91 air bleed screw, gets rid of most of this hassle. because the TV is 99.9%c closed at all times, driver out of car..
starting in 1991, the TV is closed, so all idle calibrations do not effect the TPS switch at all.. a big improvement.

the real screw on a real 89/90 is here, and added to my 89 page.

[fixkick]

keep in mind this is not a carburetor.
turn screw and adds air and engine speed rises
this is EFI
turn screw and ECU will fight you,it will correct your errors....see? that is how idle controls work , its called a SERVO system.
like autopilots, or like the tail of a kite.
or is called simply automatic idle regulation.

idle set is really not idle set, its DUTY SET !!!
but since nobody has tools to do it right, we fiddle it madly to get all speeds to work right.
in your case add tad more air,
this trick (crude) will allow the iSC to start working with head lights fully on.

---

some of the early ECU use a duty set pin that is not voltage driven at all but a special current meter.
that is calibrated for duty.
you wont get that to work. ever. as only the suzuki meter does that trick. (and 100% undocumented just for fun, dang)
the scope how ever, never is a problem ,what you see is what you get (got) WYSIWYG

[spiritofr]

Thanks fixkick, great detailed information as always!

I didn't know that turning the TV stop screw wrecks the TPS idle switch calibration. I've been playing with the TV screw a lot in the past few days, I've turned it up 1/4, down 1/4, up 1/2, down 1/2, 1/8, 1/4, etc. at least 10 times... do you think my TPS calibration is completely messed up now and needs to be recalibrated???

[fixkick]

sure
the gap is set, to .086"
when you move the throttle stop the tps calibration gap is now wrong.
this was corrected in 1991, .
when you screw the stop in, at at the point you hit the calibration point, the TPS idle switch opens and the ISC goes dead.
that is what the switch does,
so that the ECU does not attempt to fight the drivers right foot.
when you step on the gas (throttle pedal) the switch opens. and idle controls are cancelled.

these 2 years are very hard to set. up right.

---

when the switch opens,
it start working like carb. then.
idle speed is just random, (air fuel mix, friction, engine efficiency ,etc, dictate speed)

when the switch is closed, the ecu controls air supply, and that controls RPM exactly (hard coded)
on this car its a pain to set up correctly. (well they are , to one degree or the other)
on new cars, the ISC has more control and needs no fiddling.. like this..ever.
on some cars it's a huge stepper motor running a huge air valve. all under ECU control '.
but not this puppy. (like the 96 J18/j20 has or the 1999 GV V6 has)

i call this jump through 2 hoops at once.
in the 2 liter we set the TPS to 0.5v, that it, nothing else to do.