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Idle Speed Control (ISC) - By-Pass Air

  1. Measure ISC solenoid resistance. With the key off, set the DVOM on the 200 ohm scale. Disconnect ISC solenoid connector and measure solenoid resistance. If resistance is between 7 and 13 ohms, go to step 2). If resistance is less than 7 ohms or greater than 13 ohms, replace ISC solenoid and repeat QUICK TEST  .
  2. ISC short to case (ground) check. With he key off, set DVOM to the 200,000 ohm scale. Leave ISC harness disconnected, check for short from either ISC pin to ISC housing. If 10,000 ohms or greater go to step 3). If less than 10,000 ohms replace ISC solenoid and repeat QUICK TEST  .
  3. Check voltage of VPWR circuit. With the key on and engine off, set DVOM on 20 volt scale. Leave ISC harness disconnected, connect DVOM positive test lead to VPWR circuit and negative test lead to ground. Measure voltage on ISC solenoid VPWR circuit. If voltage reading is less than 10.5 volts, service harness open circuit and repeat QUICK TEST  . If voltage reading is 10.5 volts or greater, go to step 4).
  4. Check continuity of ISC circuit. With key off, leave ISC harness disconnected. Disconnect processor and inspect both 60 pin connectors for damage pins, corrosion and loose wires, service as necessary. Connect breakout box to harness, leave processor disconnected. Set DVOM on 200 ohm scale. Measure continuity of test pin 21 to ISC circuit at harness connector. If resistance is 5 ohms or greater, service open in circuit and repeat QUICK TEST  . If resistance is less than 5 ohms, go to step 5).
  5. Check for short to power. With the key off, wait 10 seconds. Set DVOM on 200,000 ohm scale, leave breakout box to harness and processor disconnected. Leave ISC solenoid disconnected, measure resistance from test pin 21 to test pin 37. If resistance reading is 10,000 ohms or greater, go to step 6). If resistance reading is less than 10,000 ohms, service short to power and repeat QUICK TEST  .
  6. Check for short to ground. With the key off, wait 10 seconds. Leave breakout box installed and processor disconnected. Set DVOM on the 200,000 ohm scale, measure resistance of test pin 21 to test pins 40,46 and 60. If resistance reading is less than 10,000 ohms, service short to ground and repeat QUICK TEST  . If resistance reading is 10,000 ohms or greater, go to step 7).
  7. Check for ISC signal at the processor. Connect processor, connect ISC actuator. Prepare vehicle for QUICK TEST  , Set DVOM on 20 volt scale. Connect DVOM between test pin 21 and pin 40. Start engine and observe the DVOM during self-test. If meter reading varies during QUICK TEST, replace ISC actuator and repeat QUICK TEST  . If meter reading does not vary during QUICK TEST, Disconnect processor and inspect for bent, damaged, corroded pins, etc. Correct as necessary. If O.K., replace processor and repeat QUICK TEST  .
  8. CODE 13: RPM does not drop to less than 1500 at end of test. Disconnect ISC harness connector, connect engine tachometer. Repeat engine running QUICK TEST  . At end of test, record service codes for future use. Does RPM remain below 1500 RPM during test? If yes, replace processor and repeat QUICK TEST  . If no, check engine vacuum hoses. Check that throttle plates are fully closed, check throttle linkage and/or speed control linkage for binding, If O.K. replace ISC actuator and repeat QUICK TEST  .
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