problem of accelerating in the begining

When ever I start my car accelerating comes down after few seconds it seems car will stop then suddenly after shocking it becomes normal but there is vibration I can feel it in steering.I showed it to Machanic he told me change the plugs I changed then he told me change the plug cable I changed then I told me change air flow cable sensor I changed Than I have been told change the fuel filter I changed then I been told to change fuel pump I changed Then I been told change the battery I changed then I been told change the mas air flow sensor I put this duplicate to see the change but same problem still is there. Can anyone can suggest me what should I do to get rid of this problem because I showed about nine mechanics but no one helped me.I don't know even mechanics do not know the problem of my car.please advice what should I do?