Controlling and managing engine idle speed

2. The figures obtained in this way are added to the correction of the coolant temperature for the entire period that the engine is warming up after cold starting.

3. The idle figure in the table is further corrected if there is a sudden drop in the idle speed (for example after a consumer is switched on).

4. In the case of deceleration and the consequent cut-off action, a subtraction is made.

5. The advance angle figure is also subject to correction in the following conditions:

   • butterfly transition;
   • return from cut-off for butterfly transition;
   • return from cut-off from engine idle speed level.

Controlling and managing engine idle speed

The adjustment of the idle speed is carried out in all operating conditions by means of the idle actuator which acts on the butterfly by-pass.

In addition to controlling the actual idle speed it also carries out the functions of a supplementary air valve and idle regulator when the various consumers are switched on (e.g. the climate control compressor); with the butterfly in the end of travel position, in effect, the actuator regulates the by-pass port compensating for the power required by the consumers in order to ensure that the idle speed is as constant as possible around the value of 860 ± 50 rpm.

The actuator fitted on this version guarantees a high degree of responsiveness during the adjustment in that the opening and closing of the by-pass are both operated by magnetic windings.

The idle is correct by means of an electronic control unit through the use of error management algorithms in relation to the speeds memorized.

The following operations are carried out:

• During idling: comparison of the actual rotation speed and the ideal speed stored in the memory depending on the value of the coolant temperature and intervention (control of by-pass port, injection time and advance angle) in order to obtain a shift value which is as close as possible to zero.
• During starting: controlling the quantity of air drawn in by the engine during starting through the position of the shutter (and consequently the useful section of the by-pass port) according to the coolant temperature and whether or not the climate control is switched on.
• During release: there are two strategies during this stage:

1. One negative strategy to decrease the quantity of fuel required by the engine (less consumption). This stage is recognized by the control unit when the butterfly potentiometer signal undergoes negative variations.

2. One dash-pot strategy to lessen the variation of the negative torque (less engine braking and less pollution). This strategy is implemented when the potentiometer signal indicates the butterfly is idling and the speed is high, conseuently the stepping motor gradually decreases the air flow rate passing through the by-pass.

Controlling cold starting

In these circumstances the mixture is naturally weakened as a result of the poor turbulence of the fuel particles at low temperatures and reduced evaporation and condensation on the internal walls of the inlet manifold, all of which is exacerbated by the increased viscosity of the lubrication oil.