Volvo: 470 GLE quits after start, side kick panel, terminal corrosion

Question
Hello,
I have a 1989 GLE that starts easily. It will operate about 20 seconds and completed quit. I noted that the tach needle will drop to 0 instantly just before when it quits.

I purchased a used distributor because I though the hall sensor was bad. Installing the replacement distributor did not help.
I uncovered the computer on the passenger side kick panel to see if there was any water infiltration.Non found. I disconnected the battery terminal and removed the gang plug from the computer, thinking there may be some terminal corrosion and wiggled it during reinstall.
That did not make any difference either.
There are times the car will run just fine for 15 minutes and then stop without any warning.
It will restart with very little effort after each one of the stoppages, but will stop again unpredictably.
The car has been sitting for the better part of 1 year because of this issue.
What suggestion can you offer.
Thanks
Robert

Answer
Robert,
Run some tests to see if you are loosing spark or fuel. If you are sure the spark is at fault, you only choice is to start replacing parts. Coil, power stage, fuel pump relay, resistor, flywheel pick up, control unit. The older cars do not have a diagnostic system to help identify what is at fault.