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Test 6: Idle Control Unit

  1. Check power supply to idle control unit (ICU): Pull connector plug off of ICU and connect voltmeter between terminal 2 of plug and ground. Start engine. Voltmeter should read battery voltage. If not, repair circuit.
  2. If voltage is correct, check ground connection of ICU: Connect ohmmeter between terminal 4 of plug and ground. Ohmmeter should read zero. If not, trace circuit and repair wiring.
  3. If resistance is correct, check speed signal to ICU at terminal 3 of plug with BMW test meter (22 13 100). If signal is not correct, trace circuit and repair wiring.
  4. If signal is correct, check for ground at terminal 6 of ICU: connect ohmmeter between terminal 6 of ICU plug and ground. With coolant temperature below 106°F (41 °C), resistance should be zero. With coolant temperature above 117°F (47°C), resistance should be infinite. If values are incorrect, check coolant temperature switch. See TEST 11 . If switch is good, trace idle control unit circuit and repair wiring. If resistance values are correct, go to next step.
  5. On automatic transmission equipped vehicles, check for battery voltage at terminal 7 of plug with ignition on and transmission shift lever in "N". If voltage is absent, trace circuit and repair wiring. If voltage is present at terminal 7, check for battery voltage at terminal 8 with shift lever in "P". If voltage is absent, trace circuit and repair wiring. If reading is correct, go to next step.
  6. On vehicles with air conditioning, check for battery voltage at terminal 9 of plug with air conditioner "ON". Trace circuit and repair wiring if voltage is incorrect. If reading is correct, go to next step.
  7. On all models, check for battery voltage at terminal 10 of ICU plug with ignition on. Voltage should be present with air temperature below 41 °F (5°C), and absent at higher temperatures. If values are incorrect, check air temperature sensor. See TEST 13 . Replace if faulty. If sensor is okay, repair wiring.
  8. If voltage readings are correct, check for ground at terminal 12 of ICU: Connect ohmmeter between terminal 12 of plug and ground. Resistance should be zero with throttle closed, and infinite with throttle open. If values are incorrect, check throttle position sensor. See TEST 9 . Replace or adjust as needed. If switch is good, repair wiring.
  9. If resistance values are correct, check ground connection at terminal 11 of ICU: Connect ohmmeter between terminal 11 and ground. Resistance value should be zero. If not, check coolant temperature sensor. See TEST 10 . Replace sensor if faulty. If sensor is good, repair wiring.
  10. If resistance values are correct, and idle control valve is good (Test 5), replace idle control unit.
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