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Home >> Toyota >> 1990 >> Celica All-Trac >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Idle Control Systems >> Idle Speed Control (ISC) System >> (3S-GTE Engine)
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(3S-GTE Engine)

  1. Warm engine to normal operating temperature. Ensure idle speed is correct. Apply parking brake, block drive wheels and place transaxle in Neutral.
  2. Unplug ISC valve connector on bottom of throttle body. Engine RPM should rise 1000 RPM or more. Plug in ISC valve connector. Engine should return to idle speed (700-800 RPM). If engine RPM does not respond as specified, check ISC valve, wiring to ECU, and ECU grounds.
    NOTE: ECU is located in front of center console.
  3. To check wiring and ECU, turn ignition on with engine off. With ECU connector plugged in, connect digital voltmeter between ECU terminals "ISC1" and "E1" from wiring side of ECU connector. Battery voltage should be present. Perform same test between "ISC2" and "E1" terminals. For more information on terminal identification, see WIRING DIAGRAMS article or PIN VOLTAGES article in this section.
  4. To check ISC valve, unplug ISC valve connector on bottom of throttle body. Using ohmmeter, measure resistance between terminals "+B" and "ISC1", and between "ISC2" and "+B". See Figure. Replace valve if resistance is not within 16-17 ohms.
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