Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Idle Speed Control (ISC) System
Engine idle speed is controlled by the ECU. The ECU contains pre-programmed information which contains specific engine speed values for different engine operating conditions.
The ECU receives signals from such sensors as the coolant temperature sensor (CTS) and air conditioner (A/C) sensor. Using this information, the ECU transmits a command signal to the ISC valve in the throttle body.
The ISC valve opens and closes the idle air by-pass to control the amount of air which by-passes throttle valve. The greater the amount of air which is by-passed around the throttle valve, the greater the engine idle speed.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.