I bought an 86 Turbo 5spd this summer. It had an electrical issue where when you switched the ignition to 'on', the fuel relay would click and buzz but if you tried to start it, it would crank but not start (no spark or fuel). Eventually, if you turned the ignition off an on several times, or leave it on long enough, the buzzing would stop, the fuel pump would engage and they you could start it.
Fix #1 I discovered that the ground from the batter was not attached to the chassis. I cleaned it and reconnected and it cleared up the problem. About a month later, the problem reappeared.
Fix #2 I realized that other things were clicking and buzzing under the hood while this condition was present. I disconnected the AAC valve solenoid and all the clicking and buzzing stopped. The car would still not start. I cleaned the connectors, reconnected the AAC and this fixed the problem. About a month later, the problem reappeared.

I have checked the engine grounds and have checked to see if the ECU is getting strong grounds on all it's grounded terminals and it checks out (< 1 ohm). While I had the ECU uncovered, I noticed that while the ignition is on and the relay buzzing is present, that the ECU will not go into diagnostic mode.When the problem resolves, it does and I discovered a few error coded (AC/ speed sensor).
Any suggestions?