"Closed loop" is a generic method of control. (Sometimes called P.I.D.)


When applied to fuelling, using a lambda sensor, fuelling corrections
for light and mid load ONLY are made automatically but only during
constant load conditions I.E. Idle, cruising etc....


When applied to boost pressure, on some cars the ecu can control exactly
the boost pressure is applied to the engine by comparing the actual map
sensor reading with a required value and pulsing a control valve (AMAL)
to regulate the boost up and down.