Abstract: An automatic control for continuing idle operation of an internal combustion engine, particularly a diesel motor, to provide proper engine conditioning before the engine is shut down. Automatic control circuitry is added by connection to the contacts of a conventional manual control switch for the engine. Normally open contacts of a relay are pre-set during engine use to bypass the manual control switch for a predetermined time following subsequent opening of the switch. A first electronic detector monitors the closing of the switch, while a second electronic detector monitors its opening. The two detectors operate both the relay and an electronic timing mechanism. The timing mechanism opens the relay contacts following a predetermined period after the opening of the manual control switch. In this way shutdown of the engine is accomplished electronically as an automatic function following the manual opening of the usual key switch.