I'm attempting to save another soldier. A salvage 94 E420, black with saddle interior.

I have almost no history on this car. Had some minor previous damage to right rear. Then a second accident where owner may have slightly glanced something on right front quarter panel. Looks too like she ran over a sidewalk. That said, with lots of cash it might be OK. Engine currently has 109k on it.

Problem: The engine runs rough.

I replaced plugs, all of which looked OK, maybe one was a touch dark (rich).
Tested Vacuum lines as best I could to the engine (I'm a total novice). All did fine.

Decided to scan codes and here is where it gets interesting. On the 38 port connector I was pulling codes. When I got to the pin 8, I heard a click. The light high pitched whine I had been hearing (I'm guessing near the MAF) stopped.

The car would not start after this. I've borrowed modules from another parts car I have and nothing helped. I've lost sleep over this trying to figure it out.
Today, I start pulling codes again. I skipped pin 8 and went through all the pins. Then I came back to pin 8. When I started pulling codes from it, I heard what can only be described as the MAF (or something near it) begin to reset and start the high pitch whine again.

The car started back to its former rough running state (sounds like it's missing on one cylinder). Before, it would not go past about 4200 rpm, which may indicate a blocked CAT, certainly inline with the accident running over something. I'm not that sure.

While I have lots of codes, most of them point to low voltage, i.e. "Voltage supply for LH-SFI control module interrupted" or "Poly V-Belt Slipping" from pin 8 (base module).

Connecting the tester to pin 13 seems to affect the pitch of the whine near the MAF, but no codes. I think this is a fuel signal pin.

Pin #19 is throwing codes relating to the vehicle speed signal missing, which as far as I know may relate to low or no voltage.

It appears to me that at least a part of the harness is new. It is a "Delphi" with an "F.D date of 31/08/2010." Hard to believe that was made in 1993.

I tested the voltage at the battery while idling, which showed 13.95 volts. I don't think it's the brushes on the alternator.

I could sure use some advice! It's one hell of a learning experience.