85 Vanagon Camper - Problem - Starts right up - drive about five or six miles and engine stops. It will crank, start and shut right down if you try to start it right away. If you wait 3 to four minutes, it will start and run. It will not repeat this for the rest of the day no matter how many times you stop and start it. It also doesn't happen every day. I changed the relays, the distributor, the oxygen sensor to no avail. Any suggestions? (not fun when it stops in the middle of an intersection)