1984 BMW 633CSi AutomaticFACTORY OEM SERVICE PROCEDURE

Test 7: 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/Kit (12 6 400 , 13 1 092 , 13 1 094 or 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 12: COOLANT TEMPERATURE SWITCH  . 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 the ICU plug with ignition on. Voltage should be present with air temperature below 41°F (5°C), and absent at higher temperatures. If any values are incorrect, check the Air Temperature Sensor. Refer to TEST 13: THERMO TIMER  . 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 10: THROTTLE POSITION SENSOR  . 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 11: COOLANT TEMPERATURE SENSOR  . 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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When to See a Mechanic

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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