[urq] Strange behavior- ECU/ignition?

[DGraber460 at aol.com]

I have over the years had my car (83 URQ) on rare occassion behave very  
strange with no clue as to why.
What happens is out of the blue, driving down the hiway at 60-70, the tach  
will suddenly to drop to zero and bounce up & down as it comes on and  off 
line. The car then backfires violently at the same time. It starts with once  
every 15-20 seconds and becomes more and more frequent until the car finally  
stops altogether. Switching the car off, and restarting (rebooting the computer)  
and all seems fine.
It has only happened 4-5 times over the years, but did it twice yesterday  as 
I was returning from the West Coast UPG in the middle of Utah, and western  
Colorado (miles from anywhere). It is not heat related, and pedal input &  
jiggling the ignition switch have no effect. Is there anything in the ECU maps,  
programs, or electronics that could cause such a thing?
This has me totally stumped!
It will go months or years between episodes- although yesterday it was 3  
hours and 240 miles apart.
 
Dennis
Denver