ME-SFI Idle Speed Control Function

ME-SFI Idle Speed Control Function

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B11/4 Coolant temperature sensor
B37 Pedal value sensor
M16/6 Throttle valve actuator
CAN Controller area network (databus)
N3/10 ME control module

The throttle valve actuator controls the idle speed by altering the position of the throttle valve. It is actuated by the ME-SFI control module.
The ME-SFI control module actuates the throttle valve motor (M16/6m1) in line with the input signals received at the ME-SFI control module (N3/10).
The throttle valve actuator controls the idle speed
- different engine loads, e.g. power steering turned to full lock, engaging Drive position, switching on AC compressor
- different mixture, e.g. from activated charcoal canister if purging activated (depending on activated charcoal charge)

Heating-up speed
In order to warm up the catalytic converter more rapidly to operating temperature, engine speed is increased in the idle speed range to 1100 - 1500 rpm for about 20 seconds after each engine start at coolant temperatures of < 40 °C. When a Drive position is engaged, engine speed is immediately controlled to a lower value.

Automatic transmission
When a drive position is engaged, a lower engine speed is controlled in order to reduce the creeping tendency of the vehicle. The information "Drive position engaged/not engaged" is transmitted by the [1][2]ETC control module (N15/3) over the CAN databus to the ME-SFI control module.

Closed throttle
To assist the idle speed control, the ignition angle can be retarded by as much as 36° crank angle or advanced by as much as 20° crank angle from the calculated specified value.

AC compressor
In order to avoid engine speed dropping in the idle speed range when the AC compressor is engaged, the AC pushbutton control module (N19) or automatic air conditioning pushbutton control module (N22) supplies a signal to the ME-SFI control module (over CAN) and the opening cross-section of the throttle valve is enlarged.

Note
The control in the idle speed range by altering the ignition angle reacts more rapidly than altering the position of the throttle valve.

Note: Idle speed can be influenced with the STAR DIAGNOSIS