[Teutone]

I put in an order for a fuel pump relay. And will be waiting for that, but in the mean time, I think im going to clean up fuse contacts and double check the grounding points.

That, plus replacing corrosion prone tin fuses with copper, should take care of some electrical gremlins, or at the very least establish a baseline to work from. I had similar issues with a distributor cap hairline crack, whenever it got a bit wet of even humid (+ check the contact spring top center.) Actually cap & rotor are the first things I change after getting an older car. Fuel filter(s), you have on your list, plus fuel pressure should be checked.
On gen II = 91 and later 190E 2.6 there is no longer a separate fuel pump relay, but a big MAS behind the battery.
When my engine died for no reason in my 91, another 2.6 specific MAS from the wrecking yard has been doing the job for the last 6 years.
In my experience, just throwing new parts at an issue can become more costly than having an experienced mechanic diagnose and fix the issue in the first place.
If you have self service wrecking yards in your area, trying used parts doesn't cost that much.

edit: another time, an idiot mechanic snoozed to tighten the nut on the bottom of the distributor, and the engine stopped.

 

[Teutone]

I agree on going for used where I can. But I believe with the parts are I ordered new are more wearables like fuel filters, relays, fuses, and ignition parts.

I do actually have new fuses, completely forgot to install them when I went for a drive.. Ill do that soon as well.

One of the former W201 moderators here used to host the manual, which included the engine versions common in North America. I have the manual downloaded on one of my laptops, but the power plug is defect, and I have no access.
Perhaps another member can help, or provide a link? I use sandboxie plus for peace of mind.

The engine turning off in the car wash, may be significant.

 

[Teutone]

I have ready signaled that and it may be a real sign of a cracked distributor cap. The synptoms doesnt necessarily improve when it s not humid but they will absolutely get worst with humidity. If you are that curious You can spray some water around the cap and see what happens. You may identify your problem that way if it s related to humidity😅

+1 The misting thingy your mom / wife use for ironing. With engine running, if water sounds a bit scary, you can also use WD40. Instead of stumbling / stopping with water mist, the engine will speed up.