1994 Sidekick RPM Question

[tmanstein]

New here
Got here because I had a fast idle, figured out it was a rat chewed vacuum hose.  While researching I removed and cleaned the ISC and replaced the gasket.  After putting all back together here is what I have:
Cold Start - 1200rpms down to 700-750.
Hot Start - 600 working up to 700-750.
This is great compared to what it was 2000cold 1600hot, so fixed the big problem but get this.
In doing the test that FixKick describes, I can remove the electrical plug to the ISC with no change at all.  I can also plug the air inlet to the ISC with no change at all.  If I read correctly it should stall/drop to 400. Am I digging too deep or do I have a problem?
1994 Sidekick 4dr, 5spd, 16Valve Gen1(I think, see pic)
Thanks in advance
Tman

[fixkick]

New here
Got here because I had a fast idle, figured out it was a rat chewed vacuum hose.  While researching I removed and cleaned the ISC and replaced the gasket.  After putting all back together here is what I have:
Cold Start - 1200rpms down to 700-750.
Hot Start - 600 working up to 700-750.
This is great compared to what it was 2000cold 1600hot, so fixed the big problem but get this.
In doing the test that FixKick describes, I can remove the electrical plug to the ISC with no change at all.  I can also plug the air inlet to the ISC with no change at all.  If I read correctly it should stall/drop to 400. Am I digging too deep or do I have a problem?
1994 Sidekick 4dr, 5spd, 16Valve Gen1(I think, see pic)
Thanks in advance
Tman

1994,  8 valve engine? or 16valves. what transmission? M/T or A/T?
the (8v sure does race idle too fast for any vacuum link from any source and vast possible)
1200rpm cold is only controlled by the IAC thermal controller in the base of 8v TB ,or the 16 is v the IAC bolted to bottom OF TB. very differently but works same. so that was all normal.
IAC is the cold engine idle controller. ISC electric is hot controls.
hot RPM is 800 RPM only +-50rpm  so 750 to 850 is normal and regulates there, ECU does regulation of it.

when you remove that ISC plug , the valve must closed 100% and that will cause  huge RPM drop if not,  the the ISC is not working at all.


ISC test 101:
hot engine 180f or more.
idle 800 is normal. never 600 ever. HOT engine.
turn on Head lamps and heater fan (not AC) at same time. and see RPM hold at 800 RPM, this proves ISC works and regulates.  it can take a second or to to catch up and hold 800. but will regulate.


if automatic trans, shifting to DRIVE from park RPM holds at 800,  or ISC is dead. if it falls far.

[tmanstein]

FixKick it is a 1994 Sidekick 4dr, 5spd, 16Valve
I removed the ISC and test off vehicle, it works as you described, blocking air when closed and letting thru when open.
I just checked and the ISC is getting constant power via the plug, should it be constant?  What regulates?

[tmanstein]

Rpm's went from 800 to 700 with headlamps and heater on.
I don't think ISC is working but not sure where to go from here as the test was good.
Note I have not touched the IAC or TB.

[fixkick]

FixKick it is a 1994 Sidekick 4dr, 5spd, 16Valve
I removed the ISC and test off vehicle, it works as you described, blocking air when closed and letting thru when open.
I just checked and the ISC is getting constant power via the plug, should it be constant?  What regulates?

ok, that works
but the ECU modulates it 200 times a second, called PWM modulation and is 50% dutycycle timed,  at 180F normal idle. (adjusted)


The 16v ISC is really the same part, only 2 pipes bent different to it. from 8v version./

one problem seen common is ISC goes dead, (it, its wires or the ECU ) and the owner hack the air bleed screw up top , rear of TB screw. then open it up to add air and hide the dead ISC.

There are only 3 ways to   see this voltage on this ISC device.
1: using a scope (any kind works)                     https://fixkick.com/IDLE-AIR/iac-wave1w.jpg
2: Duty cycle  meter, some DMM come a dial marked Duty %       https://fixkick.com/IDLE-AIR/dutycycle/2800b.JPG
3: and the harder way,  using every DMM meter in the shop set to DCV 20vdc range fixed.

some meters on DCV can see nothing at all ,  blind to 200 Hz signals due to filters or just to slow (and cheap)
better meters see the 200 Hz chopper, signal and just show the average. bingo. good meter.

the car is running and hot, at 180f (thermostat working)
the alternators is working and battery voltage can be near 15v, (or 13.3. float)
so a good DC meter will read half that for 50% duty.
or about 7vdc.

sounds hard or complex but not really. (unless broken)

connect  up the meter,
turn the bleed until 50%
done

easy pleasy lemon squeezy.? (on prefect car OTHER THINGS not wrong)


but things tend to be wrong on old cars.
any of 3 throttle cables not set to 1/2 slack, oops, (pedal, cruise cable or A/T tick down cable) you have no A;T so is  2  cables max to this TB>
or air leaks,   air leaks on 16v do not cause fast idle, it causes lean and slower, unless engine is stuck rich.
Idle is last on engine,  we fix all other bad things, first. for sure not running closed loop at idle tops that list.

now the deep woods way to set duty, (crude and only 1 tool, a screwdriver) Redneck( not said as bad word but love, nothing wrong with exiting stuck in deep woods)
hot idle. (only)
RPM too low turn bleed screew,  ccw (lets in more air) and bam ISC wakes up and 800 rpm hits, turn screw ccw 1run more extra turn for good luck.
RPM too high, just the opposite of above, and CW turned/


see related page/
https://fixkick.com/IDLE-AIR/dutycycle/9...e-air.html

[fixkick]

on 16v
air leaks (vacuum) cause lean , but id corrected by 02 sensor front (a ECU servo function) and goes normal
the the leak gets worse and o2 looses control (like most new cars) and goes way lean AFR air fuel ratio and engine slows down (for lack of fuel and attendant power)
this is 16v world.  here.
hot engine, and if closed loop works, then AFR is perfect, and minor air leaks are self adjusted.  
if the maf measures this air the MIX is always OK.
but if the vacuum leak is behind the MAF as all ARE. then it goes lean, if closed loop is lost. and engine slows.

normal leaks are
TV throttle valve.(drivers right foot)
ISC
IAC
bleed
and now others allowed.
all others are UNMETER AIR (means MAF did not measure it)  the guts are here, best drawing I annotated.
the EGR must not leak too.(it , the gasket or casing of it cracked)
many old cars leak air,(vacuum leaks) and the owners hide it by closing the bleed screw.
like a homes roof leaks so owner buys a bigger basement water pump. eeeek

[fixkick]

the 700 rpm failed, that means the ECU has no control of the ISC
on this old car step 1 is not ISC,
step one is this.:
1: insert the diagnostic jumper in the DCL pins (paperclip unbent)
2: the CEL lamp flashes code 12, for happy, other codes even lots more flash out and means failures each.

suzuki,toyota,nissan, what ever 1994 car same answer, only how to get codes varies, see?


if the ECU is in limphome mode (failsafe) idle controls are suspended, see why IDLE CONTROLS ARE LAST.


STEPS,
1: KEY ON CEL GLOWS, IF NOT FIX THIS FIRST.
2: KEY START ENGINE IF LAMP SAYS ON , THERE ARE CODES STORED. GET THEM.

HERE IS MY PAGE ON , CEL LAMP CHECK ENGINE LAMP

https://fixkick.com/CEL/CEL.html#OBD1codes

[tmanstein]

Ok. Working on it right now.
Put the jumper in without resetting, got code 24.
Then cleared by removing negative terminal and removing jumper. After 5mins connected negative and put jumper back in. Getting 12's now and took for a drive with jumper in. Note, my speedo does not work properly.
Still running 750-800 hot and dropping to 600-650 with lamps and heater on.
I have a multi meter but don't believe it will check the duty cycle.

I did find that the back side of the intake to the plenum was cracked at the hose clamps. Going to fix this and see what I have then.
Could this air leak before the air enters be my problem?

[fixkick]

Ok.  Working on it right now.
Put the jumper in without resetting, got code 24.
Then cleared by removing negative terminal and removing jumper. After 5mins connected negative and put jumper back in.  Getting 12's now and took for a drive with jumper in.  Note, my speedo does not work properly.
Still running 750-800 hot and dropping to 600-650 with lamps and heater on.
I have a multi meter but don't believe it will check the duty cycle.

I did find that the back side of the intake to the plenum was cracked at the hose clamps.  Going to fix this and see what I have then.
Could this air leak before the air enters be my problem?

24 is desd speedo.
idle controls are dead,  600 is grossly wrong.

cracks are NO GOOD. (exactly where, rear at EGR? or Right passenger side?)
sure,. that can, crack,  on mine the PO (bad guy ,hehehehe) forgot to use the top exhaust  mount plate to secure the huge intake PIPE< there,  and that caused its mounts (huge) to snap off. (sucking huge air)
and suck huge air, how it ran at was amazing, but was BAD.
no illegal air be allowed to suck in. on this engine. it can go lean fast. and not want to idle. (some even hunt the idle like yo0-yoo.

fix the trans cable too.  it's easy, kinda.  it fixes dead VSS at least  VSS is super easy clicker switch in the speedo head and never fails, it. if the head end of cable spins VSS clicks.

see that maf there, facing it , no leaks behind it, but (isc, iac, TV and bleed hole) that includes injector base cushions, too.

Some ECU (fsm) shows 24 code can on some cause limphome.  it even fuels using that as load calculations (speed)


hey you got easy ducks to knock over... 1 by 1. 



dtc-24
VSS Vehicle Speed sensor failure ,  About 4 pulses per second at 25mph = normal. Detected at Fuel cut (De-Accel)

if your gas mileage is ok, 24mpg, par,  then its not in limphome mode.  some cars go to 10-15MPG horrible in limp.

good LUCK to you !

[tmanstein]

The large pipe going into the throttle body was cracked at the connector. Order and on the way along with a new clutch cable and gear shift to fix sloppy shifting.

I have read and reread the VSS problem and am still not sure where the cable is or where I get a new one and how to replace.
Is this something that I need? This is a ranch vehicle that does not go on roads.
Thanks