D-jetronic should idle smoother than the continuous flow K and KE systems.

Continuous flow systems generally don't meter idle fuel as precisely as pulsed solenoid injectors, and KE systems maintain a stochiometric mixture at idle for emission control reasons, even though it contributes to idle roughness. Prior to emission controls, idle mixtures were much richer for a smoother idle.

At idle the fresh charge is diluted with exhaust gas and this increases with increasing valve overlap. That's why engines with "big cams" have a lopey idle. Exhaust gas dilution causes some combustion instability and misfires, and a rich mixture - on the order of 12.5:1 - results in smoother idle, but generates too much HC and CO.

Duke