I disconnected the neg battery terminal and pulled the DME. Sure enough there was what seemed to be oil on several of the terminals' wire bundles, and a film on several of the DME side connectors/housings. I can only think that somehow I drug the harness through some oil, got WD40 on it while cleaning up the plastic/rubber bits, etc. and it took a few days once hooked up to migrate down into the connections.

Hopefully this is the cause of my woes. I cleaned it all with the CRD connection cleaner and am letting it dry now. I also grabbed some mass airflow sensor cleaner and went at mine. Frankly it looked new, but my gas milage was terrible before the motor swap and from what I read the MAS can be a cause. A 20 year old sensor must be somewhat dirty at a minimum. I'll update after I get it hooked back up and try to start it.

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Current
Original owner 2002 E53 X5 4.4i to 4.6i swap
2026 G80 M3 6 spd
2025 G06 X5 50e
Former
1972 Audi Fox
1986 Saab 900S
1996 BMW Z3
1998 BMW E36 M3 Sedan
2004 BMW E46 M3
2006 Audi A3 Quatro
1993 Mopar 318 Jeep Grand Cherokee
2015 V6 Jeep Grand Cherokee