What could cause the idiot lights on the instrument panel of your 1993 Volvo 240 to come on and stay lit while the car is running when the problems indicated by the lights do not appear to exist?

This sounds like a bad alternator or bad electrical connection to the alternator. First check your battery voltage with the engine at idle. It should be about 13.6v-14.2v. All the idiot lights get their ground through the "battery" failure light. That is often caused by a bad connection of the small red wire at the back of the alternator. Most likely brushes are worn down on your voltage regulator. Replace it, fairly easy job, two screws hold it attached to the alternator. It is located next to the oil filter.