there may be two problems.

My understanding is there are two problems:

1. sometimes problem with starting the car. It seems this relates to the switch you talked about. If contact is not good, the problem may happen.

2. engine goes off on road. This has nothing to do with the switch, but may be caused by dirty gas filter, worn spark plug and wires, etc.

You can not drive a car like this, either fix it or dump it. Try DIY, on most cars, gas filter, spark plus and wire are not difficult to change.