My 1992 with 53000 miles on it has developed an unusual problem. When idling in the garage, the voltage displayed on the DIC will be 14.5 volts. The car will run fine for a while and then it is like the ignition is turned off for about 1/10th of a second. I can hear the engine stumble, the dash flickers, and the voltage displayed will drop to 12.3 or 13.6 or so for less than a second. The car will continue running and the voltage goes right back to 14.5. The fan for the AIR system will then start running. After about 1 minute or so it turns off and the car continues to run fine. Then it will happen again and the AIR fan starts running again.
Thinking it may have to do with grounds I added a ground wire from the chassis to the block and the chassis to the battery and it made no difference. I did this after looking for the ground points on the block and bell housing, and finding them. It appears that I would need to remove the exhaust on the drivers side to get to them. I never did locate the ground point on the frame that the braided ground wire from the bell housing goes to, although I did find the braided ground wire.
I also removed both battery terminals and cleaned the connections there.
Does anyone have any useful suggestions?

 

That's weird that the air fan comes on like that? That is possibly a bad relay. Did you check out your alternator?

 

Check the connections at the alternator. Mine was acting a bit funny - on start up my volts were at 10'ish and it was running poorly (and the main fan came on immediately). When I touched the plug on the alternator it smoothed out and volts were back to 13.9.
Cleaned the corroded connection, applied dielectric grease, and all is well.