Had valve cover gasket changed in my Infiniti i35 and car will sometimes shake and rpm flutter. Check engine light came on day after replacement

Hello, it sounds to me that when the coils were removed to replace the valve cover gasket(s), it may have caused an issue with the boots that secure the coils onto the spark plugs. The coils or boots (if available) may need to be replaced on affected -- or all -- cylinders. Testing should be performed to see which ones are misfiring.