M102 doesn't start when humid or after a rain

[muller]

The engine turns but wouldn't fire. If it ever does, it will die out within a minute or when the car is put in gear.
The car runs perfectly in all other circumstances, even when warm.
Items replaced:
OVP
Ignition coil
Ignition wires
Spark plugs
Distributor and cap

Checked fuel at the fuel distributor test terminal and it's flowing.

[pawoSD]

Have you verified spark in these conditions? Might be something else like fuel pump relay or other electrical in the vehicle acting up.

[muller]

Yes @pawoSD, I did swap the fuel relay. I happen to have three units that I collected while on junkyard runs. No improvements!
EZL was bone dry as well.

[oldsinner111]

wiring?

[Usaguy]

Do a smoke test to check for vacuum leaks.

What do the plugs look like?

[muller]

@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.

[Frank Reiner]

m:
For the sake of information, what version of M102 is involved, and in what chassis?

[muller]

@Frank Reiner, it's a 2.3 L in a W201 (1988).

[muller]

Could it be a build up of condensation in the intake, and if so, how to mitigate?