Toyota Repair: Sienna check-Engine light flashing, engine misfire, scantool

Question
Mine is doing the same thing - Check engine light comes on after driving a while and engine runs rough.  It actually quit on me today. It started back up and got me back home. Taking it to Toyota dealer now.  No codes showed up when I took it in last week. Local repair shop could not find anything wrong either.  Runs for several days without the check engine light coming on.  Seems to be mostly when climbing hills.

Answer
Thye check engine light usually flashes because the catalityc converter is overheating which in turn is most likely cause by an engine misfire as you have already stated, the light may not stay on but it will flash when the misfire occurs, the computer should be checked for pending trouble codes or the van driven with the scantool connected to get live data so the cylinder that is misfireing can be identified, usually it's a coil/igniter malfunction but they have to find out which one is the cause.