@oldsinner111: ignition cables are new. I checked the harness, no cracks (unlike the junk in W140 and w124 from the 90s).
@christuna: I did a pressure test on the intake. Nominal!

By the way, the CIS altitude sensor is fairly new (behind the batter). I replaced that one while chasing a dying issue of the car that was losing power while driving in the rain. That resolved it. This was a few years ago.