1987 Mercedes Benz 560SLFACTORY OEM SERVICE PROCEDURE

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.
Chapter Navigation
Return to Chapter: Component Testing
Factory Service Tools

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.

Shop Manual-Ready ToolsCompare Repair QuoteQuote Shield Pro

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.