Toyota Repair: 04 Sequoia Backfires, air fuel ratio, toyota sequoia

Question
My '04 Toyota Sequoia w/ 16K miles has backfired several times.  Seems to happen when I accelerate.  I called Toyota dealership to schedule appt.-- the service guy asked if I had just driven by -- he heard me.  I took vehicle in as suggested.  Then he says "well... if the check engine light is not on and it's not backfiring now, there's nothing we can do"  -- he's the one who heard it.  Is there some sort of computer they can use to diagnose a problem like this?  

I use Chevron or BP gasoline. And have used at least two full tanks since I intially noticed the problem. Also, I have followed maintenance schedule like clockwork.

Basically, from what the dealership said, I should wait until I have done further damage or until it breaks down before they will even look at it.  He said, "don't worry, it's under warranty".  That's fine...I don't want to be stranded out there w/ kids in the car.

Thanks!


Answer
I'm not sure why there is backfiring, normally a lean or rich air fuel ratio will turn the check engine light on, you can ask the dealer to hook up the diagnostic scantool to see if there are any pending trouble codes in the computer, they can also look at the fuel trim readings to check for a problem with the fuel mixture, it is also possible that you may have gotten some contaminated fuel.