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Home >> Mercedes Benz >> 1993 >> 300CE Cabriolet (124.066) L6-3.2L (104.992) >> Repair and Diagnosis >> Powertrain Management >> Computers and Control Systems >> Relays and Modules - Computers and Control Systems >> Electronic Throttle Control Module >> Description and Operation >> Electronic Accelerator or Idle Speed >> W/O ASR

W/O ASR

Cruise Control/Idle Speed System Diagram:





IDENTIFICATION
Vehicles equipped with ABS only (no ASR) use a cruise control/idle speed control module (N4/3).

PURPOSE
The cruise control/idle speed control module (N4/3) controls the cruise control and idle speed functions to insure smooth and consistent operation regardless of engine temperature and load.

OPERATION
When the ignition switch is in the ON position, the idle speed control function is in operation. The position of the throttle valve for the idle speed is determined by the control module via the nominal value potentiometer (accelerator pedal input) in the cruise control/idle speed actuator (M16/2). The actual value potentiometer in the cruise control/idle speed actuator, signals the position of the throttle valve. The cruise control/idle speed control module compares the signals and specifies the position of the throttle valve via the output signal. This signal is used by the cruise control/idle speed actuator to adjust the throttle valve.

Before starting the engine, the throttle valve position is determined by the engine temperature. Once the engine is running, the idle speed is controlled by the cruise control/idle speed control module which provides a constant idle RPM, compensating for engine temperature and load.

The cruise control/idle speed control module uses the following information to determine the throttle position:


Idle speed control function
The idle speed control function uses the following information to determine the correct idle speed:
^ Engine speed (TN-signal)
^ Coolant temperature
^ Vehicle speed signal
^ Selector lever position
^ A/C compressor engagement signal

Idle Speed/Temperature Chart:





During idle, the control module keeps the engine speed at a constant RPM depending on engine coolant temperature.

Warm-up RPM Chart:





Warm-up Control Function
The warm-up control is effective at all engine temperatures. After each start-up (accelerator pedal in idle position) the engine increases the idle speed for approx 20 seconds. Below 20 °C (68 °F) the engine speed is 900 - 1000 RPM.

A/C engagement Control Function
When the A/C compressor is turned on, the throttle valve opening is increased before the A/C compressor engages. This keeps the engine idle speed at a nearly constant RPM.

















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