What causes a vehicle to “stall”, during operation? The problem seems to disappear, then re-appears!
There can be a number of causes. On older cars, the idle setting on the carburetor could be out of adjustment. On newer cars, the sensor(s) controlling the idle speed may not be functioning right.
If you give us more details on your make, model, year, mileage and maintenance history of yoyr carm, we can perhaps give you more specific answers.