Engine problems of the 2006 Lexus IS250

I was operating my 2006 Lexus Is250 awd at very low speed in a parking lot when the engine began to surge. I could not bring the car to a stop using the brake pedal and could barely keep it from creeping forward. I shifted into neutral and the engine really began to roar, revving very high, but I was then able to stop the car and turn it off using the stop/start button. When I restarted the car it operated normally and the problem did not re-occur. The floor mat had nothing to do with the problem, as it was a factory mat held in place by the little hooks, and was not the all weather mat. The mat was in place after the incident. I reported the occurrence to my dealer, warnock Lexus, in livingston, n. J. They checked the car out and found nothing wrong and no evidence of anything wrong in the computer's memory. The problem did not recur and the car was returned to Lexus at the end of the lease. I now have a 2009 Is250 awd and am concerned about the reports of this problem. I don't feel the floor mat had anything to do with it. The date below is approximate, but Lexus should have a record of the incident from the dealer service department.