The recent engine swap has to be the clue here.

Also, when you substituted the resistor for the sensor by putting it in the connnector, you write "When I put a 10,000 ohm resistor in the connector..." making me wonder if you pushed the resistor wires into the terminal ends.

But the sensor (black housing for LH2.4 instead of blue) is a dual thermistor connected each pin to ground (threads into head). Don't use a blue sensor or get tricky with teflon tape.

One half (one pin) serves the ICU, while the other half is what you're tracing to 13 on the ECU. Ground is wired separately in the harness to the ring terminals attached to the fuel rail bolts.

It is very likely in a swap, a ground wire is left undone. Or the connector is not making good contact on the sensor. Regardless of the reason, your car will have one heck of a time doing warm-up enrichment without that sensor making the adjustment in the ECU. You need to see its resistance back at the ECU pin 13 to ground or it won't function.
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Art Benstein near Baltimore Crrrrazy Ray's!