vapor lock only happens when your engine is already hot and you are trying to restart it...reason is the fuel in the injectors and injector lines gets hot and boils...however once its running it is not a problem b/c new fuel is pushed through the injectors cooling them

the psssst...you hear when undoing the gas tank is the result of heat that expands the liquid fuel and air in the gas tank...(only when it is warm out, the car has been running for long periods, or the car was driven hard)

vapor lock is unlike boiling ones brake fluid b/c the gasoline is burnt and constantly refreshed by cooler fluid...where the brake fluid has no avenue to cool properly (besides brake ducts)

when starting a cold engine there is no vapor lock and releasing pressure in the gas tank does nothing...it is probably distributor or main relay acting up...there is another post in this forum