Engine surges (rapid acceleration) while in motion. The engine starts fine and will normally accelerate fine; however, while in motion or maintaining a steady speed the engine surges (rapid acceleration). I can hear the engine rev and the rpm's jump from 2 to 3 - 4 and back. Engine light does not go on. Dealer has scanned the vehicle and found no error codes, nor has dealer detected any leaks. Intemittent surging, does not occur daily. Cruise control does not operate consistently, when the cruise control does operate it automatically shuts upon upon engine surge (rapid acceleration). Fuel economy is down. I had the fuel pressure regulator replaced and fuel injector cleaning and throttle body service. Any ideas?