1994 Sidekick RPM Question

[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