If it's not one of the sensors and it truely is vapor lock than you are probably missing the fiber washers that insulate the injecter mounts from the heat of the head. I had vapor lock problems and this was the cause. It is a common problem when your mechanic is not familiar with these cars and throws those little washers out or replaces them with metal. There should be eight of them. They go under and over the mount to prevent contact with the head and the bolt. Thickness is important so buy ones that are made for your car. If you replace these you will also need new seals for the mounts. These seals are not usualy in the injector seal kits so you need to buy them separately. Although I do sugjest getting the the seal kit too since you will have the old ones out anyway and most of the time they are dried up and need replaced anyway.

Thad
Seattle