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Test Dd - Idle Speed Control

NOTE: If engine is running rough or has rough idle, correct these conditions before performing test. Causes may be in ignition system, fuel system or EGR system. If fuel system problems are encountered, go to TEST T - FUEL CONTROL  , step 1) through 9).

To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault: engine temperature not up to operating temperature, engine over operating temperature, A/C input (electrical problem), improper idle speed/throttle stop adjustment or cruise control linkage.

  1. Turn key off. Connect engine tachometer and start engine. Disconnect Idle Speed Control (ISC) harness. If RPM drops or if engine stalls, go to next step. If not, go to step 3).
  2. If EGR service codes 31, 32, 33 or 34 are displayed, go to KEY ON/ENGINE RUNNING CIRCUIT TEST MENU  table and perform appropriate CIRCUIT TEST  . If these codes are not displayed, go to next step.
  3. If service codes 22, 41, 42, 33, or 34 are displayed, go to KEY ON/ENGINE RUNNING CIRCUIT TEST MENU  table and perform appropriate CIRCUIT TEST  . If these codes are not displayed, go to next step.
  4. Turn key off. Disconnect ISC solenoid. Set DVOM on 200-ohm scale, and measure resistance of ISC solenoid. If resistance is between 7 and 13 ohms, go to next step. If resistance is less than 7 ohms or more than 13 ohms, replace ISC solenoid and repeat QUICK TEST  .
  5. With key off and ISC harness disconnected, set DVOM on 200,000-ohm scale. Measure resistance from either ISC pin to ISC solenoid housing. If reading is greater than 10,000 ohms, go to next step. If reading is 10,000 ohms or less, replace ISC solenoid. Repeat QUICK TEST  .
  6. Leave ISC harness disconnected. Turn key on, leaving engine off. Measure voltage between VPWR circuit at ISC harness connector and battery ground terminal. If reading is less than 10.5 volts, repair open in circuit and repeat QUICK TEST  . If reading is 10.5 volts or more, go to next step.
  7. Turn key off and wait 10 seconds. Leave ISC harness disconnected. Disconnect ECA 60-pin connector. Inspect connector for damaged pins, corrosion, or loose wires. Repair if necessary. Install breakout box, leaving ECA disconnected. With DVOM on 200-ohm scale, measure resistance between test pin No. 21 and ISC circuit at ISC harness connector. If reading is greater than 5 ohms, repair open circuit and repeat QUICK TEST  . If reading is less than 5 ohms, go to next step.
  8. Turn key off and wait 10 seconds. Leave ISC harness disconnected. Install breakout box, leaving ECA disconnected. Set DVOM on 200,000-ohm scale. Measure resistance between test pin No. 21 and test pins No. 40, 46, and 60. If any reading is less than 10,000 ohms, repair short to ground and repeat QUICK TEST  . If all readings are 10,000 ohms or more, go to next step.
  9. Turn key off and wait 10 seconds. Leave breakout box installed. Leave ECA and ISC solenoid disconnected. Set DVOM on 200,000-ohm scale. Measure resistance by connecting DVOM negative lead to test pin No. 21 and positive lead to test pin No. 37. If reading is greater than 10,000 ohms, go to next step. If reading is 10,000 ohms or less, repair short to power and repeat QUICK TEST  . If code or symptom are still present, replace ECA.
  10. With key off, connect ECA and ISC. Leave breakout box installed and set DVOM on 20-volt scale. Connect DVOM between test pins No. 21 and 40. Start engine and observe DVOM while slowly increasing and decreasing engine RPM. If DVOM reading varies, go to next step. If DVOM reading does not vary, replace ECA and repeat QUICK TEST  .
  11. Verify curb idle speed. If curb idle speed is within specifications, replace ISC and repeat QUICK TEST  . If curb idle speed is incorrect, check engine vacuum hoses for proper routing. Use emission label as a guide. Ensure throttle plates are fully closed. Check throttle and/or cruise control linkage for binding. Repair if necessary. If these items are okay, replace ISC and repeat QUICK TEST  .
  12. Turn key off and wait 10 seconds. Deactivate SELF-TEST. Start and run engine at 2000 RPM for 2 minutes or until top radiator hose is hot and pressurized. Turn key off and wait 10 seconds. Perform KOER SELF-TEST. If code 17 is displayed, inspect throttle body and air inlet for contamination. Clean if necessary. If okay, adjust curb idle speed and repeat QUICK TEST  . If code 17 is not displayed, service other codes as necessary.
  13. Code 13, High RPM Check. Turn key off. Connect tachometer to engine. Start engine. With engine running, disconnect ISC harness connector. If engine RPM drops or if engine stalls, replace ECA and repeat QUICK TEST  . If engine RPM does not drop, check engine vacuum hoses for proper routing. Use emission label as a guide. Ensure curb idle is correct. Make sure throttle plates are fully closed. Check throttle and/or cruise control linkage for binding. Repair if necessary. If these items are okay, replace ISC and repeat QUICK TEST  .
  14. Code 48 Displayed. Check for and repair holes, cracks, and/or bad connections at air cleaner outlet tube (between vane airflow meter and fuel charging assembly). Perform KEY ON/ENGINE RUNNING (KOER) SELF-TEST  . If code 48 is displayed, check for other sources of unmetered air. If code 48 is not displayed, EEC system is okay, go to KEY ON/ENGINE RUNNING CIRCUIT TEST MENU  table and service other codes as necessary.
Fig 1: Idle Speed Control (Air By-Pass) Circuit
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