Hello,
After backing out of my driveway, putting in forward and getting ready to
accelerate I heard a light backfire.
After about 15 minutes of driving the Techmeter dropped to below zero.  
Felt a bump in the transmission as I drove down the road and the "Check
Engine" light came on.  The cabin became warm but (imagination ?) the
temp. gauge was at normal.

Pulled the Sonata over, checked the oil, tranny. fluid and water.  All
were okay.

Anybody have any idea what may be the problem?  This happened before on
the way to work on an especially hot and humid day.  Same condition with
this event.

Any clues?

Thanks in advance!