I'm trying to diagnose if my problem is vapor lock or something else. Once the summer temperatures hit, my 1989 300SE will just stall while driving. Usually happens within the first 5 minutes or after a refuel. I sit for a few & try to re-start. It may take about 5 minutes for the car to restart. Also note, that the car does not get peppy until it's running for about 5 minutes or driven a short distance. Is this vapor lock or something else? How can I solve?