W/O ASR

Cruise Control/Idle Speed System Schematic:

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

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

LOCATION AND I.D.
The cruise control/idle speed control unit is located in the module box (F23) and is color coded light orange.

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 unit 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 unit 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 unit which provides a constant idle RPM, compensating for engine temperature and load.

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

Input signals
^ Base module overvoltage protection (N16/1)
^ ABS control unit (N30)
^ LH control unit (N3/1)
^ EZL/AKR ignition control unit (N1/3)
^ Cruise control/idle speed control actuator (M16/2)
^ Stop lamp switch (S9/1)
^ Starter lockout/backup lamp switch (S16/1)
^ Cruise control switch (S40)
^ A/C compressor engagement signal
^ Data exchange via controller area network (CAN)
^ Wheel speed sensors (L6/1 - L6/4)
^ Diode matrix (V2)

Output signals
^ Cruise control/idle speed actuator (M16/2 with throttle valve)
^ LH control unit (N3/1)
^ Impulse readout (malfunction memory) via 38-pole diagnostic socket (X11/4)
^ Data exchange via controller area network (CAN)

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 unit 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. Between 20 °C (68 °F) and 30 °C (86 °F) the engine speed is 800 - 900 RPM.

DIODE MATRIX SIGNAL
When additional consumers are turned on (e.g. A/C, heated seats, rear window defogger), an engagement signal is transmitted to the diode matrix (V2) for RPM increase. This signal is passed on to the cruise control/idle speed control unit to increase the idle speed.

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.