ME-SFI Idle Speed Control Function

ME-SFI Idle Speed Control Function

ENGINE 120.982 /983




B11/10 Right ECT sensor
B37 Pedal value sensor
M16/3 Right EA/CC/ISC actuator
M16/4 Left EA/CC/ISC actuator
N3/11 Left ME control module
N3/12 Right ME control module
CAN Controller Area Network (databus)
d, e Idle throttle information

Task
Controlling idle speed in the case of
- 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)

Operation
The EA/CC/ISC actuator controls the idle speed by altering the position of the throttle valve. It is actuated by the ME-SFI control module.
The right ME control module (N3/12) operates the throttle valve actuator motor (M16/3m1) in line with the input signals at the right ME control module (N3/12) and at the same time transmits information via the CAN databus to the left ME control module (N3/11), which thereupon operates the left throttle valve actuator motor (M16/4m1).
Idle speed information is exchanged between the ME control modules over two cables. If the CAN databus fails, the idle speed is thus regulated.

Heating-up speed
In order to warm up the catalytic converter more rapidly to its operating temperature, engine speed is increased for about
20 seconds to approx. 1110 - 1500 rpm at coolant temperatures of
< 40 °C each time the engine is started with the selector lever in position P/N. 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 ETC control module (N15/3) over the CAN databus to the ME-SFI control module.

Ignition angle in idle speed range
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 or automatic air conditioning pushbutton control module (N22) supplies a signal to the ME-SFI control module (as of approx. 6/96 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 STAR DIAGNOSIS/HHT.