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Home >> Mercedes Benz >> 1987 >> 560SL >> Repair and Diagnosis >> Engine Performance >> System >> BOSCH Cis-E System >> Component Testing >> Engine Idle Speed Stabilization
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Engine Idle Speed Stabilization

  1. With engine at idle speed and operating temperature, place selector lever in a driving position. On 420 engine, idle speed should be about 575 RPM. On 560 engine, idle speed should about 525 RPM. If not okay, go to step 2). If okay, test is complete.
  2. With shift lever in "P" or "N", measure voltage at idle speed control unit terminal No. 12. Move shift lever to "D". Voltage should drop. If not, repair circuit or transmission switch. If okay, test is complete.
  3. With engine at idle speed and operating temperature, turn A/C compressor on. Place selector lever in "P" or "N" position. On 420 and 560 engine, idle speed should be about 675 RPM. If not, go to step 4). If okay, test is complete.
  4. Connect test cable to idle speed air valve. Set multimeter to mA scale. Start engine and run at idle and operating temperature. Engage and disengage A/C compressor. When engaging A/C compressor the current at idle speed air valve should increase approximately 60 mA. If not, repair circuit according to wiring diagram. If okay, test is complete.
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