Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
1987 Mercedes Benz 300SDLFACTORY OEM SERVICE PROCEDURE
Idle Speed Control
- With engine idling, remove 2-pole connector from electromagnetic actuator for 3 seconds and reconnect connector. When connector is reconnected, idle speed should momentarily increase above idle speed specification. Testing is complete. If idle speed does not increase, go to next step.
- Apply battery voltage to electromagnetic actuator for 3 seconds. Idle speed should increase. If voltage is applied longer than 3 seconds, actuator will be damaged. If idle speed increases, proceed to next step. If idle speed does not increase, replace electromagnetic actuator.
- Run engine at idle speed. Disconnect 2-pole connector from electromagnetic actuator. Connect multimeter and set to volt scale. Probe and check voltage at connector terminals. Voltage reading should be 12 volts. If voltage is to specification, proceed to next step. If voltage is not to specification, check for open circuit in wiring or blown overvoltage protection relay fuse. If no open circuit or blown fuse is found, replace EDS control unit.
- With engine idling, remove 2-pole connector at electromagnetic actuator. Check idle speed. Idle speed should be 530-610 RPM. If idle speed is to specification, testing is complete. If idle speed is not to specification, adjust idle speed. See IDLE SPEED ADJUSTMENT table.
IDLE SPEED ADJUSTMENT
| Trimming Plug Position | Idle Speed (RPM) |
|---|---|
| 1 | 550-590 |
| 2 | 570-610 |
| 3 | 590-630 |
| 4 | 610-650 |
| 5 | 630-670 |
| 6 | 650-690 |
| 7 | 680-720 |
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.
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.