I am not sure what the problem is. I bought a used Altima GLE. I had trhe engine mounts replaced, the valve cover gasket changed and new plugs, wires, cap/rotor and air filter.

It seems that the car has a vibration when it is idleing, the mechanic that did the work has told me, it could be bad gas so I should use a fuel injector additive and it should get better over the next few months.

There are codes that came up,
1. P0440 Evaporative emission control system small leak, negative pressure
2. P1448 Vent control valve.

The mechanic says these have nothing to do with the vibration/idle issue.

Is it possible the work he did may have caused this??