DW, I also have an 89 244 with 189K miles and had a similar problem but not exactly. I had an error code 221 (fuel system compensating for extreme lean or rich mixture at cruse)intermitantly with terrible idle. This happend especially when the engine was warm.

My problem turned out to be fuel injector wire harness chafing along the intake manifild . I installed some sheet silicone with wire ties to hold it in place so the harness wiring doesen't touch the sharp edge of the intake manifild. It seems that after all the miles the insulation "cold flowed" and allowed a short to the engine.

Also if I were you I would check the connector of the mass air sensor for corossion. If you see any, scrape the pins with some emery cloth and install some electrical insulating grease (Auto Zone) to help prevent any moisture from oxidizing the pins again.