it really is simple ,kinda.
the 200 hz square wave to the ISC,
a perfect motor, with no air leaks, (illegal) has a 50 % duty cycle at the 2 pins of the ISC at 800 RPM.
such that, if you lowwer the motor, RPM down (alternator loads , ir drive with a A/T)
the RPM starts to drop and the duty goes up.
that i,s the time open is longer, say from 50 % to 70% and rpm stays at 800.
if all is perfect and working
you adjust the bleed screw to 50% duty.
as you adjust the screw the ISC /ECu corrects the RPM by changing air flow and holding 800RPM.
there are 3 pins associated with duty on the DLC, a jumper to ground and output duty pin.
try this with a volt meter running, 0v is 0% duty 7v is 50% and 14v is 100%
hot idle, no accessories. idle tps switch closed. at 0v
http://www.fixkick.com/CEL/DLC/DiagJump.html
jumper pin 2 and 4 on DLC next to right front head lamp shell.
connect volt meter from 4 to 6 , 20vdc meter range, the ECU outputs duty to this pin, in diag mode.
adjust the bleed for 7vdc. 50 % Duty is 7v, (fsm steps)
if the idle does not hold to 800 there is an air leak or the isc is sticking or leaking.
optionally you just throw a scope on to the ISC pins and set bleed for 50% .
the period does not change only the duty. period is .005 seconds.
Fsm states "the duty is not less than 28% (or more than 72% if it's OFF Duty measurement)" 28% is a massive air leak.
that is 22% above and below 50% ,that. that is the sweet spot to stay in,, IMO.
here is mine. at ISC pins actual and is set wrong, low = valve closed, i have an air leak here.
1.5x 2 (converts to %) shows 30% barely good, but too close to 28.% i got leaks.
or counter to that, the 3.5ms low x2 is70% low, the ECU is closing the ISC 70% of the time to cure air leaks.
this is cold motor, if hot this is bad duty.
![[Image: iac-wave1w.jpg]](http://www.fixkick.com/fresh-air/iac-wave1w.jpg)
sorry you have a 8v isc for 96 , 16v,
i do not know the damage that might happen if those screws are removed. but id not want to send it back at todays postage rates. id try to get the screws out gently.
pen. oil or heated.
how could, duty go wide open 90% percent or more.
easy, EGR leaking the ECU opens ISC WIDE open to save stalling idle.
the 200 hz square wave to the ISC,
a perfect motor, with no air leaks, (illegal) has a 50 % duty cycle at the 2 pins of the ISC at 800 RPM.
such that, if you lowwer the motor, RPM down (alternator loads , ir drive with a A/T)
the RPM starts to drop and the duty goes up.
that i,s the time open is longer, say from 50 % to 70% and rpm stays at 800.
if all is perfect and working
you adjust the bleed screw to 50% duty.
as you adjust the screw the ISC /ECu corrects the RPM by changing air flow and holding 800RPM.
there are 3 pins associated with duty on the DLC, a jumper to ground and output duty pin.
try this with a volt meter running, 0v is 0% duty 7v is 50% and 14v is 100%
hot idle, no accessories. idle tps switch closed. at 0v
http://www.fixkick.com/CEL/DLC/DiagJump.html
jumper pin 2 and 4 on DLC next to right front head lamp shell.
connect volt meter from 4 to 6 , 20vdc meter range, the ECU outputs duty to this pin, in diag mode.
adjust the bleed for 7vdc. 50 % Duty is 7v, (fsm steps)
if the idle does not hold to 800 there is an air leak or the isc is sticking or leaking.
optionally you just throw a scope on to the ISC pins and set bleed for 50% .
the period does not change only the duty. period is .005 seconds.
Fsm states "the duty is not less than 28% (or more than 72% if it's OFF Duty measurement)" 28% is a massive air leak.
that is 22% above and below 50% ,that. that is the sweet spot to stay in,, IMO.
here is mine. at ISC pins actual and is set wrong, low = valve closed, i have an air leak here.
1.5x 2 (converts to %) shows 30% barely good, but too close to 28.% i got leaks.
or counter to that, the 3.5ms low x2 is70% low, the ECU is closing the ISC 70% of the time to cure air leaks.
this is cold motor, if hot this is bad duty.
sorry you have a 8v isc for 96 , 16v,
i do not know the damage that might happen if those screws are removed. but id not want to send it back at todays postage rates. id try to get the screws out gently.
pen. oil or heated.
how could, duty go wide open 90% percent or more.
easy, EGR leaking the ECU opens ISC WIDE open to save stalling idle.
http://www.fixkick.com