Adaptive Equipment problems of the 2003 Chevrolet Malibu

After my 2003 Chevrolet Malibu had been parked in the sun for a while, on a short trip of 4 miles, the car started reving up and taking off on it;s on. It also caused my a/c hose to burst (I am convinced it is related). I took it to dealer for repair and they cleaned the throttle and replaced the a/c hose. There is still the same problem. It seems as though it happens when it is very hot weather and I am making short trips running errands which calls for turning engine off and restarting. I drove back home with my foot entirely on the brakes while trying to keep the car from running out of control. I am very reluctant to drive it now, until I can find someone to "really" fix the problem (as I was stuck with a $487 repair bill).