1991 Opel Astra Home Used Engine Placed Recently Now Off Sometimes Even Car

Home used engine was placed in recently. Now engine goes off sometimes even when the car in in motion - and i engage the brakes or put it in free. When that happens sometimes i can start right back; other times it would not even crank and would start by bushing the car. Some mornings you i start the engine stays on for awhile and goes off by itself.

Also, the engine shakes in about every 3 seconds and the car jerks especially when moving on first and second gears. I expect the car to move smoothly and freely when it is left in first or second gear. But it jerks badly in first gear, as if it wants to get back to reverse.