car shakes when i turn it on put it in drive i have to give it gas and its slow going turns of when stopped at light

took car to mechanic he said it was misfiring so he changed 1 coils and 6 spark plugs car drove off half way home same problem turns off engine shakes,took back to mechanic he looked it over got 6 different codes he turned off codes drove it for 40 miles was good got it back to shop same thing they now have to car 5 days cant find what it is they checked the timing on it all good checked filters good, changed some other part good car still shakes and now he does not get any readings on codes out of idea's help any suggestions

thank you
lou