I too, let a 1990 GL sit for two months, starting and running the car every two weeks or so while a buyer waited for her payment to arrive.

When she took delivery, the car died once, wouldn't start once, and had several instances of warning lights.

I told her to drive the car for a week. All the troubles went away, and she has driven the car for almost two years without any similar ills.

I think that the various electrical connectors need the vibrations and movements that they go through when the car is driven over the road. Try to clean and grease as many electrical connectors as you can.

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3 8s & 2 7s 725,000 miles total