GF07.61-P-2008MLK ME-SFI Idle Speed Control Function

GF07.61-P-2008MLK ME-SFI Idle Speed Control Function
- refinement package
- as of model year 09


Idle speed control function requirements, general
^ Circuit 87M ON (engine control ON)
^ Engine running
^ Accelerator not operated

Idle speed control, general
The idle speed control regulates and stabilizes the idle speed according to operating conditions and engine load.

For the idle speed control, the ME-SFI control unit (N3/10) reads the following sensors and signals:
- Crankshaft position sensor (L5), motor speed
- Hot film MAF sensor (B2/5), engine load
- Coolant temperature sensor (B11/4)
- Electric controller unit (VGS) (Y3/8) over engine compartment CAN (CAN C), gear range
- Comfort AAC control and operating unit (N22/7) over interior CAN (CAN B) and engine compartment CAN, status of air conditioning system

Idle speed control function sequence
The ME-SFI control unit controls the idle speed by means of throttle valve actuator (M16/6) and adjusts the injection time of fuel injection valves (Y62) according to changes in the air mass.
To assist the idle speed control, the ME-SFI control unit can shift the ignition angles of the ignition coils (T1) towards "retard" by up to 20° crank angle, or towards "advance" by up to 20° crank angle.

Adjusting the ignition angle enables a faster response than adjusting the throttle valve.

The ME-SFI control unit adjusts the idle speed in the following operating and engine load conditions:
^ Warm-up phase function sequence
^ Selection of gear range "D" or "R" function sequence
^ Refrigerant compressor cut-in function sequence (A9)
^ Purging function sequence

Warm-up phase function sequence
In the warm-up phase, the ME-SFI control unit controls idle speed, according to coolant temperature, in order to bring the catalytic converters more quickly up to operating temperature after engine start.
Additional function requirements in the warm-up phase are:
- Coolant temperature <40 °C
- Gear range "N" or "P" engaged

The ME-SFI control unit raises the idle speed to about 1100 to 1300 rpm for about 20 s.
After this time has elapsed, the idle speed is increased at a coolant temperature of < 70 °C in line with the temperature for approx. 50 seconds by approx. 50 to 100 rpm.

Gear range selection "D" or "R" function sequence
When gear range "D" or "R" is engaged, a lower engine speed is set in order to reduce the tendency of the vehicle to creep forward.

To do this, the ME-SFI control unit evaluates the information from the electric controller unit (VGS) about the selected gear range.

Refrigerant compressor cut-in function sequence
So that the engine speed at idle does not drop when the refrigerant compressor cuts in, the comfort AAC control and operating unit (N22/7) sends a CAN signal to the ME-SFI control unit before cut-in. The ME-SFI [ME] control unit adapts the idle speed appropriately.

Purging function sequence
The idle speed control prevents any change in the engine speed due to purging.

Diagnosis
The basic setting of the idle speed can be read out and influenced using the DAS.