Intermittent Check Engine Light?

The first time the check engine light came on was at highway speed. The car jolted and light came in shortly after. Light remained on and car had slightly rougher idle than normal at city speeds. By the time I was home, the idle had returned to normal and the check engine light went away. Toyota diagnostics found a Code 12 (OBD-I). The technician stated that he found nothing out of the ordinary when driving the car, and the CEL was not illuminated during the test. No repairs were made, Toyota recommended replacing the spark plugs, wires, and distributor. Recently, the CEL has reappeared. This time it appeared without any jolting or noticeable drivability changes and went away by the time I got home. CEL was on for roughly 15 minutes before turning off again. No CEL on startup, only after periods of driving. Car is able to start normally and idles normally. I’ve had a previous Code 12 approximately 2 years ago, unsure if this code was ever cleared from the system. Any information helps! Thank you.