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Idle Rpm Check

  1. Checking Idle RPM. With ignition off, disconnect SELF-TEST jumper or unlatch STAR tester. Connect tachometer and start engine. Ensure engine temperature is greater than 128°F (53.3°C). Check engine RPM. If engine RPM is 750-850, go to next step. If engine RPM is not within specification, go to step 3).
  2. Checking "Cold Engine" RPM. Turn ignition off. Connect tachometer and disconnect Engine Coolant Temperature (ECT) switch. Start engine and check RPM. If engine RPM is 1150-1250, and problem was low or no idle, replace ECT. If engine RPM is not to specification, go to step 6).
  3. Check Engine Temperature. Run engine for 2 minutes at 2000 RPM. Ensure upper radiator hose is hot and coolant temperature is greater than 128°F (53.3°C). Rerun step 1). If engine RPM is between 750-850, ISC system is functioning properly, check carburetor adjustments. If idle speed is not within specification, go to next step.
  4. Checking ECT Switch. With key off, disconnect ECT connector. Set DVOM on 200-ohm scale. Engine temperature should be greater than 128°F (53.3°C) and switch should be closed. Measure resistance of ECT switch. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, replace ECT switch and rerun SELF-TEST.
  5. Checking Continuity of ECT Circuits. Turn ignition off and disconnect ECT switch. Disconnect ISC-E processor 24-pin connector. Inspect and repair connection as necessary. Set DVOM on 200-ohm scale. Measure resistance between pins No. 9 and 24 (ground). Measure resistance between sensor harness connector and ground. If both resistances are less than 5 ohms, replace ISC-E processor. Reconnect ECT switch and rerun SELF-TEST. If resistance is greater than 5 ohms, repair open circuit and rerun SELF-TEST.
  6. Checking ECT for Short to Ground. With ignition off and ISC-E processor disconnected, inspect and repair pin contacts as necessary. Disconnect ECT harness connector. Set DVOM on 200,000-ohm scale. Measure resistance between pin No. 9 and chassis ground. If resistance is greater than 10,000 ohms, replace ISC-E processor and retest. If resistance is less than 10,000 ohms, repair short to ground and retest.
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