1. Warm the engine.
Start the engine and let it run for a few minutes until it has reached its normal operating temperature.
2. Locate the idle adjustment screw.
The idle adjustment screw is usually located on the side of the throttle body. It is a small screw that typically has a plastic cap on it.
3. Remove the plastic cap.
Some idle adjustment screws may have a plastic cap on them. If so, remove it to access the screw.
4. Adjust the screw.
Use a screwdriver to turn the idle adjustment screw clockwise to increase the idle speed or counterclockwise to decrease it.
5. Check the idle speed.
Once you have made an adjustment, check the idle speed using the tachometer on the dashboard. The ideal idle speed for the 1984 Mercedes 300SD is 700-750 RPM.
6. Repeat as needed.
Repeat steps 3-5 as needed until the idle speed is at the desired setting.
7. Replace the plastic cap.
After you have completed the adjustments, replace the plastic cap on the idle adjustment screw.
8. Test drive the car.
Finally, take your car for a short test drive to ensure that the idle is set properly.
