Idle/Throttle Speed Control Unit: Testing and Inspection

1982 Chevrolet Citation V6-173 2.8L VIN X 2-bblSECTION Testing and Inspection

Fig. 031 - Chart C-2A Idle Speed Control (ISC) Check.:






1. ECM functional test--ECM should cycle ISC in both directions when the test terminal is grounded.
2. ISC plunger functional test--light should go ON when plunger is depressed.
3. Voltage should be near battery voltage.
- Checks for open in circuit to ISC.
- Low or no voltage indicates an open to the ECM, faulty ECM or poor ground.
4. Manually applies voltage to the ISC motor to determine if fault is in motor.
5. Checks for faulty P/N switch circuit.
- In park or neutral, voltage is normally low.
- In drive ranges voltage goes to near battery voltage.



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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.