Two recent incidents I had might be informative -

1 - engine began to ran roughly time to time. A couple of times it set code 123 (ECT sensor signal missing or faulty).

2 - One day without warning the car suddenly would crank ok but not even try to start.

In case 1 I found that the connector to the ECT was corroded. ECT itself was ok.

In case 2 the main relay was not actuating (you can tell because the idle air motor will not run unless relay works). One of the wires to the relay coil was nicked and it corroded there, leaving the circuit open.

I mention these because they may be the kinds of incidents that become more frequent with aging, and because it did not turn out necessary to replace the main parts (and in fact it wouldn't have done any good).

Also, quite a few people have in the past observed that the connections to the mass air flow sensor can become corroded too, resulting in erratic operation.

A great new year to all!