ISC Valve - what voltage?

[Nordic92]

I posted at beginning of September (CEL on and no code) - still did not find my problem...
Resume:
- when engine get warm, idle drops (normal) but CEL turn on = code 34: MAF sensor; I had change the MAF sensor but still the problem is there.
- timing is good;
- compression is good;
- fuel pressure is good;
- TPS is good (resistance);
- ECU is good (I tried another one from friend);
- EGR is good (and cleaned now!);
- injectors are good;
- no air leak;
I'm running out of possibility...
I'm left with the ISC valve. I tested the resistance: ok
I removed it and try it on battery : ok, it operates normally
But: while the ISC is on, I unplugged the wire, and I get reading between 0 and 1V at idle and goes up to only 2V when I open throttle (5000RPM) . I'm surprised to get only 2V??? what should be the reading? I tried to blow air in by the hose: the valve is closed, it does not open for sure. I got a second ISC, had one in place, and had the second one plugged to the wire and in my hand; I was expecting to see it operates (open/close), but nothing happenned; even when I open throttle, the valve does not move at all.
Engine, cold or warm, does not burn the gas good - it miss sometimes and smell very bad. I removed the ISC - too much fresh air I agree - but then the engine run perfectly and burn its gas good (controlling manually the air intake with a sheet of metal).
I know I get the code 34 but testing MAF and changing it, it's good.
ISC does not operate, only get 0 to 2V: is this normal??
thanks,

[mpo]

ISC is driven by PWM signal, so ordinary voltmeter will show you false readings.

[fixkick]

x2 the PWM answer, but some voltmeters on DC RANGE can read about 7v (1/2 of 14vdc alt voltage) at 50% duty cycle, others are blind,(meters)
the ISC moves 200 times a second, humans can not see things that fast, just a blur.

but is moot point, to look.
34 is bad, MAF, bad wires to maf, or bad ECU.
you never used the voltmeter to test the maf, to see why the 34s are there, per my maf test page.
most used (find in yards, or wrecks or junk boxes off fleabay) MAF's are in fact bad, they are over 22 years old. but easy to test on car.
Fact 1, the ECU did not lie, reset the dome fuse, clears 34s; if it comes back, the 34s are REAL.

fact 2, 34s put the ecu in to (failsafe) mode. the ECU is now emulating, mimicking the maf, it's hopeless this path. horrid MPG too.

http://www.fixkick.com/ECU/LimpHome/failsafe.html

the ISC controls idle speed, not fuel ratio's at all, the maf inputs, become the fuel ratio (+02 controls hot @idle and not accelerating)
as they say, first things first. you are trying so hard to ignore the dead maf. why?

my fail safe page, really is just a copy of FSM , plus other facts. tells you that when in failsafe mode, the ISC will be dead. that is how it works.
It is a fact,3, that failsafe, kills idle controls (ISC), when catastrophic errors happen, like a DEAD MAF.

the ECU KNOWS the MAF mimic failsafe mode, can not control idle well so , it just does not try.

off my maf page. (using a back probing needle, got this?)
is ground good to the maf
is 12vdc good (power) to the the maf?
the voltage key on, no start is [color=#FF0000]1.0

[Nordic92]

MAF test results
Key on:
Blue-black - should read 12.6V; read 11.9 (OK, so many tests, battery is not fully fully charged)
Black: should read less than 0.5V; read 0V
Grey-Black: should read 1 to 1.6; read 1.3V
Engine running:
Grey-Black: should read 1.7 to 2 at idle; read 1.8
Open throttle:
Grey-black: should read 3V on neutral; read about 2.5 to 2.7

The ISC valve clicked when the key is turned on but does not seems to do nothing after.
So looks like the ECU talks to it, but does not get signal from the MAF???
Black wire: I was surprised to get a <perfect> 0 - what is that wire doing in the operation of the MAF - could that be that wire be cut or off somewhere?
I tested my other MAF (yes, second-hand...): they all read similar with the grey-black wire but always the black at <perfect> 0

[fixkick]

pin1 black is ground, 0v
pin 3 blue-bk is power and will most likely run all down to near 9vdc. so it can work as the battery slowly dies. by design.
pin2 gray stipe ,is the output. and is good, so you failed to reset the DTCs and this MAF code is a very old , data no longer, valid?'

those are good signals. dont forget some MAF are intermittant, so tap the side gently when reading pin 2,, does it drop out, that is a bad mAF>
isc is not to be messed with until 34s clear, 34s, kill all ISC actions, during failsafe. you need to learn to clear the dtcs.
pull the dome fuse , count to 5min, and put back.
now see if 34s are clear, sure they are, they must.
then run the engine and be sure 34s dont come back, if they do that gray wire is cut.


the black wire is ground
the MAF is just and electronics board, like the car radio.
it has power and ground, if either fail the circuit has no power supply,
if the ground opens this pin jumps to battery voltage instantly. and the MAF goes to sleep.
same with the 12vdc pin, if it drops below 8v, the maf goes to sleep, goes, DEAD< until power restores.
we need to put 34s to bed, reset the ECU, using the dome fuse, pull..... this must be cured.
and the CEL lamp never stop looking at it, running, it must be out.
i suspect you are not OBD1 savvy, ? all cars have this and all need to be reset the same way. even hondas. and toyoto's and GM .
the only differ. is what fuse to pull.

DOME.

here is a china POS MAF
but shows how they work clearly

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DOME = ECU memory pin, the NVRAM power, when allowed to drop to 0v, (or near) it forgets every thing.

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now the ISC, the isc only runs idle speed, that is all it does. mostly.
it does other tricks you may never notice, like you cutting throttle fast, in a lower gear and the ECU uses the ISC to prevent driver neck snap,(anti-excessive, deceleration)
it also is used to fast idle, say A/C on.
it just keeps the idle steady. It does not , mix fuel ,it does not.

there are many things that cause it to fail or to be OVERPOWERED. (Ill pretend it works)
1: Fail safe mode kills it dead. (yes, DTC 34 and most others)
2: TPS idle switch not closed.
3: gross under or over injection of fuel.
4: id does other tricks with A/T but yours is M/T
5: gross air vacuum leaks, or IAC stuck wide open hot.

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I am not clear on all your symptoms, just 34s;
idle too high or low , 800 hot is normal.?
engine misfiring.?
lost engine power/?
????

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The ISC , is pretty must useless at cold start.
the IAC is wide open so the ISC can not over power that gaping air hole
then the IAC closes near 150f
and now the ISC is in command, if the above errors are not happening.
the ECU just watches, RPM and if the RPM drops to say 700 for 1sec, it open the ISC, or if the RPM rises to say 900, it then closes the ISC and returns idle to 800
this action is call and electronic servo, not unlike air craft autopilot, or cruise controls.
the ECU does simple close the valve, if it did that rpm will fall like a brick to 400 rpm and stall.
so the ECU MODULATES it with a 200 hz (read 200 cycles per second) PWM square wave signal, the DUTY CYCLE of said wave, changes the air flow in the ISC.
on a stock hot good engine the duty cycle is about 50% set at the factory (via the bleed screw in the TB)
its set there. by calibration.
if no scope, one can use a DC meter and set it to 7vdc. using said bleed, but some meters, hate 200HZ and are blind to it. or are so slow, during this a/T conversion cycle the meter
is again blind to these pulses.... YMMV your meter may vary.

there are only 3 tools that work, any scope and any real suzuki Duty meter, only 2.. but there are meters sold that do in fact measure this. or a DMM with a duty mode.

step one is no 34s
then step 2 is TPS test.

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keep in mind we dont have a real scan tool here.
so are working blind
we must do all the tests of all sensors. to find if and input is wrong. first.
the long hard way.
that is why a 1996 car is more easy to fix. a $9s scan tool works. wonder.s

[Nordic92]

not getting better...!!!
code 34 used to come when engine was getting warm (when the rev dropped from 1500-2000 to 800-900 after few minutes)
then when engine was cold, CEL was gone, I was able to get my code 34
This morning, I tested the MAF, played with the TPS and the coil; now the CEL is always on and even when cold, engine revs at +-1000
Reset ECU does not change anything
ISC opens for 1/2 sec but at the minute (or at the second I should say...) the CEL gets on, it closes back = ?
So I feel that I touched something else this morning...
TPS: I unplugged the 4 wires, started engine; ok. Give throttle; no difference (still with the TPS unplugged) as when it is on so I feel the permanent CEL I get (that I cannot get code for) might be the TPS.
From the TPS wires with key on; readings are: A(bottom) :0V B:5V C:0V D(top):5V - ----- 5V??? normal?
I tested the TPS directly (resistance) as mentioned on your site : all ok. I suspected wiring between TPS and ECU - is there anything between TPS and ECU
I will try with another TPS and see if any change

[fixkick]

unplugging the TPS is wrong, that forces it to 2 times failsafe. why unplug sensors.? all that does is confound matters and tests..
no the TPS wires directly to the ECU.
what are all DTC codes, and do not unplug sensors, that causes the ecu to store DTC errors, of that action and then goes to failsafe.
a prime goal is to avoid failsafe, not cause it.

my tps page shows the fsm pages and how to do the calibration. on all years.
16v, pre 96's TPS.
bottom is pin 1, top is pin 4.
so pin 1 is ground, so 0v is perfect.
the pin 2, is (idle switch) is 5v this is wrong , someone removed the TPS and put it back , and never calibrated it. must be 0v.! at idle. or just key on.
the pin 3, is 0.5v, TP pin, must be 0 to 1v is normal keyon. or idling. (about) but never near 5v)
the pin 4 is , 5.0v that is power supply pin called 5vdc from ECu that provides power here and is 100% normal.

so there is why IDLE fails because some one fiddled the TPS willy nilly. or worse screwed on the never touch TB stop screw. (the throttle valve is 100% closed and this screw is never to be touched, there)
http://www.fixkick.com/sensors/tests/TPS...html#MYWAY


are you still getting 34s,??? please report what you get, for DTCs all of them. after the DOME reset, all things connected.

have you examined the ECU pin that is B8
gray-black this is he MAP pin. it must not be a corroded pin on ECU or cut wires here.
examine both pins, (at ECU and MAF) for damage, and key on and back probe this eCU pin and that voltage must match what is at the MAF, same color, if not the wire is cut.
this is a simple test. its just a wire. (maf output)
http://www.fixkick.com/ECU/92-95MPI-eng-...e-huge.png
here is the FSM page, showing the same pin, B8
see it?
http://www.fixkick.com/specs/95ecu2w.jpg