WHAT WOULD CAUSE MY SONATA TO SOMETIMES REV UP HIGH WHEN APPROACHING A STOP?

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THE PROBLEM UNFORTUNATELY IS INFREQUENT, MAYBE 6 TIMES PER MONTH. DEALERSHIP DOES DIAGNOSTIC CHECK AND NO ERROR CODES EXIST. HAD PROBLEM OVER TWO YEARS NOW. DEFINETLY A SAFETY ISSUE AS UNLESS ONE BRAKES QUICKLY CAR WOULD REV UP THROUGH A STOP SIGN INTERSECTION. (WHEN PROBLEM OCCURS IT ALWAYS REV'S UP AS I APPROACH A STOP, NEVER WHILE STOPPED.)