Harness problems in an old 700 Turbo are certainly a possibility. Any cars before 1988 could have the problem. And weird running usually does result.

Also black smoke, super-rich running and bad mileage usually are also caused by intake leaks. If you're sure that's all ok, no holes in any hoses, ok, we can eliminate that and look for other stuff.

How about a temp sensor? The coolant temp sensor, if failed or disconnected, tells the computer that it's stone cold, and it compensates the way a carburetor uses its choke: make the mixture super rich, and keep it that way until the temp sensor says "I'm warm now". But maybe it never shows a warm engine to the computer.

The temp sensor is under the intake manifold. It's easy to miss or possibly not get a plug all the way into its socket. Have a good look at that. If the donor engine came from a different "family" of fuel injection, i.e. crossing the LH 2.2/2.4 divide, then this sensor would have to be changed in order to plug into your car's harness. I did this last year, installing a 1989 240 engine(LH2.4) into a 1988 740 NA (LH2.2). Easy swap, but access is worse on an assembled engine.

Good luck with it!
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