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Home >> Pontiac >> 1981 >> T1000 2D Hatchback, Automatic Trans >> Repair and Diagnosis (Single Page) >> Engine Performance >> Tune-Up >> Tune-Up - 4 CYL >> Idle Speed >> Slow & Fast Idle Adjustment (2.5L Only) >> Idle Speed (With Idle Speed Control)

Idle Speed (With Idle Speed Control)

  1. Engine idle speed is controlled by Idle Speed Control (ISC) motor and Electronic Control Module (ECM). Adjustment is not normally needed.
    NOTE: If idle problems are encountered, see General Motors Computer Command Control in COMPUTERIZED ENGINE CONTROLS Section.
  2. If a new ISC motor has been installed, or if diagnosis indicates adjustment is needed, use the following steps to adjust high and low limits for ISC motor.
    CAUTION: Do not disconnect or connect ISC connector with ignition on, as ECM may be damaged.
  3. Connect tachometer to engine. Connect dwell meter to green mixture solenoid test lead (near carburetor). Set dwell meter to 6-cylinder scale. With A/C off, run engine until dwell meter begins to vary (closed loop operation).
  4. Turn ignition off and unplug ISC connector. Connect jumper wires to pins "C" and "D" in motor side of connector. Connect pin "D" to ground and apply 12 volts to pin "C". Motor will retract. Disconnect wires as soon as motor reaches end of travel.
    CAUTION: Always remove voltage as soon as motor reaches end of travel. Do not apply voltage to pins "A" or "B", as damage to internal switch will result.
    Fig 1: Idle Speed Control Motor Connections
    G09317544Courtesy of GENERAL MOTORS COMPANY
  5. Start engine and run until dwell meter begins to vary (closed loop operation). Place transmission selector in "D", then adjust idle stop screw for minimum RPM.
  6. Place transmission selector in "N". Apply 12 volts to pin "D" with "C" grounded. Plunger will extend. With plunger fully extended, turn plunger to obtain maximum RPM. Apply voltage to pin "D" again with "C" grounded to check plunger extension.
  7. Turn ignition off. Disconnect jumper wires and reconnect ISC connector. Start engine and place fast idle screw on top step of fast idle cam. Adjust fast idle to 2600 RPM.
  8. Remove test equipment. "Check Engine" light will come on to indicate adjustments have been made. Disconnect ECM fuse for at least 10 seconds to erase trouble code and light.
NOTE: Battery cable can be disconnected to accomplish code memory erasing. However, if battery cable is disconnected, memory will be lost in electronic radio, trip computer, clock, and other devices. To avoid having to reset these items, use ECM fuse if possible.
Idle Speed Control Adjustment

Application Minimum RPM Maximum RPM
2.5L
  Man. Trans 930-950 2000
Auto. Trans 630-650 2400
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