Checking the vacuum regulator (Mercedes-Benz S-Class W126)

Whenever the engine is loaded more heavily at idle and the speed drops, for example when a gear is engaged or the air conditioning system is switched on, the vacuum regulator ensures that the idle speed is increased until the engine returns to its previous stable state.

The same test instructions apply to checking the vacuum regulator as for adjusting the idle speed.



Remove the vacuum hose (69) and close with a suitable plug.

Loosen the adjusting screw lock nut (79) while holding the threaded rod with a 6 mm open-end wrench.

Set the engine speed to 1250 rpm using the adjusting screw (79). Attach the vacuum hose.

Using a flat feeler gauge, check whether there is a gap of 0.5 mm between the adjusting screw (79) and the throttle lever (12). If not, adjust the gap using the adjusting nut (78). On vehicles with an automatic transmission, apply the handbrake and engage the gear. If equipped, fully engage the power steering. The engine should still run smoothly; otherwise, adjust the speed using the adjusting nut (78).

If available, turn on the additional air conditioning system. The vacuum regulator should now rise completely and connect the throttle valve, slightly opening it. The engine should run steadily.

Connect the temperature switch plug.