I'm not aware that the '89 configuration is different than my '88 190E 2.6, but mine has a vacuum line from the manifold to the EZL. Most of it is that 3 mm white nylon tubing, but there are short, molded rubber hoses at both ends to connect the nylon tube to the nipples at both the inlet manifold and EZL.

The EZL has a sensor that converts manifold vacuum to additional spark advance (basically an electronic version of the old mechanical vacuum advance "can"), but it's disabled by a signal from the throttle position switch when the throttle is at the idle position. At idle, timing is fixed by the EZL at 9 deg. BTC and is not adjustable.

Duke