Chuck, I think you are right and your memory is sharp. The relay is well known to 240 owners, to the point many have one in their glove box.

Could indeed have been the relay.

Here's how:

The FI relay switches two circuits. The "system" circuit powers everything in the fuel system -- injectors, air mass meter, idle motor, and the fuel computer itself. The "pump" circuit powers the fuel pumps and the oxygen sensor heater.

The only function the ECU, or fuel computer, performs when not powered by the system relay is retention of stored trim and code memory. That's all it has power to do, directly from the battery. When the ignition key is turned on, a simple circuit in the ECU picks the system relay, which powers the remainder of the ECU and keeps it powered after the key is shut off, long enough to do the cleaning of the hot wire in the air mass meter.

If the system relay portion had a cold solder, the whole computer might suffer unstable power. Operation would be unpredictable. If the pump relay portion had the flaky solder, the fuel delivery might be questionable, as well as the oxygen sensor heat, resulting in a mixture control failure -- the 113.

I have to emphasize, the 113 is not an indictment of the oxygen sensor itself. Many other faults can result in the oxygen sensor providing feedback which prevents closing the control loop. This includes a laundry list of vacuum leaks, exhaust leaks, fuel pressure faults, AMM, temp sensor, and electrical faults such as poor ground wiring -- or what I'm dealing with today -- rusty spin flange at the cat. Anything that can screw up the mixture after warm up.
--
Art Benstein near Baltimore

No wonder nobody comes here; it's too crowded. (Yogi)