The "economy" gage is just a vacuum gage. The left side limit of travel is 0.585 bar and the red zone begins at 0.4 bar (1 bar = 14.5 psi/29.5" Hg), so the limit is about 17" and the red zone begins at about 12".

My erstwhile '84 190E five-speed idled on the LH stop. My 2.6 doesn't quite reach the stop because it has more valve overlap (300E has the same camshaft), and it doesn't generate as much idle vacuum (16-16.5" Hg.) Never measured the 2.3 but it was probably around 18".

Reducing revs or increasing load - such as having the auto trans in drive or engagement of the A/C compressor will reduce idle vacuum.

Mercedes eliminated the gage because people didn't know how to use it and many owners were confused by it's readings. I wish they calibrated it in bar so I could read actual manifold vacuum.

Duke