Toyota Repair: 2002 Sienna Start Problem, factory warranty, vapor lock

Question
I've had several instances where my Sienna won't start. It sounds fine when turning over - but never fires or starts up. Both times I have had it towed to the dealership - it then starts for them and continues to start - so they have me pick it up saying they can't locate the problem until it fouls out for them. This has happened to me 4 times now. On several instances it will start if we put the gas peddle to the floor. It also seemed to work once when I unscrewed the gas cap (thought maybe I had a vapor lock). The dealership says everything appears to run fine.  

Answer
There is a known problem with the idle speed control valves on these engines, it may still be under the factory warranty, ask the dealer to replace the idele speed control valve, the warranty period for the valve is 3yrs/50,000 miles in most states in the US.