2006 Other Chevrolet Models Engine idle speed problem and en

My car is Chevrolet Optra 2006, I have experience that the engine at idle , the speed intermittently goes high to about 1500rpm and the engine is vibrating when I reach at approx. 80 kmh. I have change the spark plugs and fuel filter also the oil is recently change but still same problem exist. The problem has been check by the Chevrolet shop but the problem keeps coming back after sometime. please advice