1988 Plymouth Colt BaseFACTORY OEM SERVICE PROCEDURE

Idle Speed Control & Throttle Position Sensor

  1. Engine coolant temperature should be 185-205°F (85-95°C). Turn lights, cooling fan and accessories off. Place transmission in Neutral or Park. Place steering wheel in straight-ahead position and loosen accelerator cable.
  2. Turn ignition switch to "LOCK" position. Connect White connectors (labeled "CHECKER") of Harness Connector (MD998452 ) to ECI checker. Connect harness connector to ECU and body side harness connectors.
  3. Connect voltmeter to terminals of ECI checker marked "EXTENSION". Set switch on ECI checker from "CHECK METER" to "EXTENSION" position. Set check switch to "6" position and select switch to "A" position.
  4. Turn ignition on (do not start engine) and hold 15 seconds or more. This will set ISC motor at idle position. Turn ignition switch to "LOCK" position. Disconnect ISC servo motor connector. Put ISC motor in idle position.
  5. Open throttle valve by hand 2-3 times and allow it to return with a snap each time. Loosen fixed servo adjusting screw. See Fig 1 . Start engine and run at idle. Check engine speed and motor position sensor output voltage. Engine speed should be 700 RPM. Output voltage should be .9 volts. If not to specification, adjust using ISC adjusting screw. See Fig 1 .
  6. Tighten fixed servo adjusting screw until RPM increases. Loosen screw until RPM ceases to drop, then tighten screw 1/2 turn.
  7. Stop engine. Turn ignition on (engine does not start) and check TPS output voltage. Voltage should be .48-.52 volt. If not to specification, loosen TPS screws and adjust by turning (clockwise increases voltage). Tighten screws after adjustment.
  8. Set check switch of ECI checker to "OFF" position. Turn ignition switch to "LOCK" position. Carefully separate connectors of ECI checker from ECU and body side harness connectors. Connect body side harness connector to ECU. Adjust accelerator cable. Connect ISC motor connector.
  9. Start engine and ensure idle speed is correct. Turn ignition off. Disconnect battery for 5-6 seconds to erase diagnosis memory. Reconnect battery.
Fig 1: Adjusting Screws Location
G61397
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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.

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