I have a '78. I had a problem like that once.

I found that a relay about one inch square on the battery side fender that had gotten moisture inside it. It was corroded enough to work intermittently for the longest time.

This relay controls two separate circuits simultaneously. The frequency valve that should buzz when running and the 0-2 sensor path to the ECU.

The valve controls the fuel mixture. It appeared to effect a warm or hot start when it didn't work properly. It also ran a little crappy at idle which may have been for the lack of 0-2 sensor information.

Just a thought and it was rare as things go. Thought it may be worth a try.

Phil