now what idle speed means. EFI, 1989 g16 up.
The ECU sets idle speed not you. (in a servo controlled closed LOOP) if ISC is dead the stop screw does change idle RPM, and is the clue #1 ISC IS DEAD. (a fix first issue for sure)
The ECU is hard coded (accessories off) to 800RPM -+50rpm and regulates there, via said loop.)
The ECU does this magic using only (hot engine) the ISC valve solenoid top right of TB. 2 wires. ISC = idle speed controls.
The ECU modulates this from 1 to 100% at 12vdc. this 200Hz modulation is called DUTY Cycle.
Duty cycle is set to 50% hot.(by shop calibration steps) engine using the TV stop screw (far bottom screw)
this adjustment means the ISC can lower or raise the RPM by 50% of its authority. (revolutions per minute, or R/min)
about 400rpm range of control but varies. by age of engine and say vacuum leaks. oops..
what this magic does is when the engine runs too slow the ECU sees that as spark RPM drop and the ECU opens the ISC to gain 800 rpm back.
this is also used with AC turned on and rpm goes to 900 to 1000 RPM by ECU command, (RPM varies by year car ECU)
that is how ISC works, in brief.
The ECU sets idle speed not you. (in a servo controlled closed LOOP) if ISC is dead the stop screw does change idle RPM, and is the clue #1 ISC IS DEAD. (a fix first issue for sure)
The ECU is hard coded (accessories off) to 800RPM -+50rpm and regulates there, via said loop.)
The ECU does this magic using only (hot engine) the ISC valve solenoid top right of TB. 2 wires. ISC = idle speed controls.
The ECU modulates this from 1 to 100% at 12vdc. this 200Hz modulation is called DUTY Cycle.
Duty cycle is set to 50% hot.(by shop calibration steps) engine using the TV stop screw (far bottom screw)
this adjustment means the ISC can lower or raise the RPM by 50% of its authority. (revolutions per minute, or R/min)
about 400rpm range of control but varies. by age of engine and say vacuum leaks. oops..
what this magic does is when the engine runs too slow the ECU sees that as spark RPM drop and the ECU opens the ISC to gain 800 rpm back.
this is also used with AC turned on and rpm goes to 900 to 1000 RPM by ECU command, (RPM varies by year car ECU)
that is how ISC works, in brief.
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