today when i started my car... it started ok.. then i start to hear 'pop' sounds from the exhaust...then i rev the engine.. it hesitated to rev till bout 3k rpm then it rev better but still not normal... and when rev my car sound like impreza.. i dont think its miss firing.. so decided to drive to workshop.. it kept jerking so i decided to boost.. then it felt better but still not normal... then suddenly after driving for awhile it came back to normal.. soby the time i got to my workshop it was normal.. my mechanic check all the hoses he said ok.. anyone experience this before? pls advise..