Friends - 1989 W124 wagon, 220K, well maintained, new fuel relay and pumps/filter (relay had failed) and OVP (precautionary) recently.

Car is dying at speed and once or twice at idle. Like it's losing spark (e.g. different than when fuel pump relay would cut out). Sometimes if you coast it will 'catch' and you keep going, more often I pull over, turn off ignition, sit for 10-30 seconds, and it starts right back up and off we go. Averaging 1-3 times per day of this happening.

Car has original O2 sensor, check engine light comes on then goes off the past 2-3 months, I have a replacement but haven't had/made the time to put it in. Can a failing/failed O2 sensor cause the above? Based on my experience I'm thinking either the coil or crank/flywheel sensor. Where would you start?

THANKS many times for any advice.

Brian