09-13-2019, 11:11 PM
The ECU forms a servo action, a closed loop, control that has control of hot idle at all times foot off the throttle and idle switch in TB closed at 0vdc at the TPS pin called idle pin.
The ECU then takes command of idle and can get lost , (means loss of servo control)
if there is a huge air leak (aka, vacuum leaks) the air leak tiny is hidden by the ISC (and o2 sensor) and the pulses to the ISC go more closed to hide said leak.
if the combined (crude estimate) is a leak that adds up to more than say 400 rpm? the ISC (actually the ECU) looses control and goes dead. (8v car like to hunt idle. speeds illegally)
the HOT RPMs are then near 1000 or more.
THEN the next horror happens (hacking)
the owner of the car (or others) would then unknowingly turn the bleed screw in, and set the idle back to 800. ending all ISC controls forever.
the cure is find the leaks and end them then re-calibrate duty cycle. of the ISC.
in the last drawing, the MAP is not on your 16valve engine , the drawing does both engines 9/16v, and I have bypass lines drawn to show my tricky universal drawing.
The TV must be 99.9% closed, it is so closed in fact that water will not go past it , TB in hand, you pouring water to the brass TV valve. plate. (feeler gauge 0.0005" clearance)
All air leaks must be found and corrected.
once all air leaks are corrected the DUTY must be set, to 50% hot idle, never cold, never below 180F. coolant, (ECT reads 300 ohms hot)
all modern cars work the same way until car has throttle by wire,(no TV cables !)
many do not use solenoid ISC but use a stepper motor there, seen on vast jeeps. but work the same way exactly.
The test for the ISC is easy, (basic) is just get engine to 180f, idle switch closed, 0v, and overload the Alternator.
on M/T car, Headlamps on and blower heater on at same time or even rear defrosts glass heater on if present.
or A/C car , shift to drive. engine stalls or goes way to low not 800 RPM (750 is spec min.) ISC is dead. (means the servo is dead, why only remains)
on M/t same rules 750 is spec, min. allowed the ISC is touch slow and can take 1 second for it fully gain control of you actions.
that is all there is on ISC.
as any engine gets older vacuum goes lower, and the ISC corrects this, with more open , PWM, the Servo has limits on how many leaks it can hide.
The ECU then takes command of idle and can get lost , (means loss of servo control)
if there is a huge air leak (aka, vacuum leaks) the air leak tiny is hidden by the ISC (and o2 sensor) and the pulses to the ISC go more closed to hide said leak.
if the combined (crude estimate) is a leak that adds up to more than say 400 rpm? the ISC (actually the ECU) looses control and goes dead. (8v car like to hunt idle. speeds illegally)
the HOT RPMs are then near 1000 or more.
THEN the next horror happens (hacking)
the owner of the car (or others) would then unknowingly turn the bleed screw in, and set the idle back to 800. ending all ISC controls forever.
the cure is find the leaks and end them then re-calibrate duty cycle. of the ISC.
in the last drawing, the MAP is not on your 16valve engine , the drawing does both engines 9/16v, and I have bypass lines drawn to show my tricky universal drawing.
The TV must be 99.9% closed, it is so closed in fact that water will not go past it , TB in hand, you pouring water to the brass TV valve. plate. (feeler gauge 0.0005" clearance)
All air leaks must be found and corrected.
once all air leaks are corrected the DUTY must be set, to 50% hot idle, never cold, never below 180F. coolant, (ECT reads 300 ohms hot)
all modern cars work the same way until car has throttle by wire,(no TV cables !)
many do not use solenoid ISC but use a stepper motor there, seen on vast jeeps. but work the same way exactly.
The test for the ISC is easy, (basic) is just get engine to 180f, idle switch closed, 0v, and overload the Alternator.
on M/T car, Headlamps on and blower heater on at same time or even rear defrosts glass heater on if present.
or A/C car , shift to drive. engine stalls or goes way to low not 800 RPM (750 is spec min.) ISC is dead. (means the servo is dead, why only remains)
on M/t same rules 750 is spec, min. allowed the ISC is touch slow and can take 1 second for it fully gain control of you actions.
that is all there is on ISC.
as any engine gets older vacuum goes lower, and the ISC corrects this, with more open , PWM, the Servo has limits on how many leaks it can hide.
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