968 Cabriolet L4-2990cc 3.0L DOHC (1993)
Engine Control Module: Description and Operation
Digital Motor Electronics (DME) Control Unit
OPERATION AND LOCATION
DME unit is mounted in front passenger's footwell behind footrest board. Unit is encoded by free plug bridge, located next to DME connector, on
control unit wiring loom. If plug bridge is vacant, DME control unit is regulated by lambda control. If a 1k ohm resistor is inserted in bridge, DME
control unit operates without lambda control.
On model with Tiptronic transmission, engine wiring harness is different from manual transmission models. DME unit is informed that auto trans is
fitted. With selector lever is in PARK or NEUTRAL, idle speed is 880 ±40 rpm. When trans is shifted into gear, idle speed is modified to 840 ±40
rpm.
To reduce shift impact when under load, engine ignition timing is briefly retarded depending on engine speed and load, when transmission shifts up or
down. This reduces engine torque momentarily. This occurs if Tiptronic control unit introduces a shift process in transmission and a signal is sent to
DME unit. DME briefly retards spark.
ADAPTIVE SYSTEMS
DME has several adaptive system including lambda control, cylinder filling control, and knock control. DME unit will lose its adaptive memory and
any stored fault codes, if battery or control unit connector is disconnected and engine must run for about 10 minutes at normal operating temperature
after the next start for control unit to adapt anew.
