Hello and thank you for using Just Answer
upper intake manifold leak can set this code
if you use a can of carb/throttle body cleaner you can spray around the intake while it is idling if the idle raises up you have found a vacuum leak
make sure there are no vacuum leaks around the engine and all hoses are connected
if you have a leak the idle will raise when you spray the cleaner on it.
have you asked the mechanic to double check for vacuum leaks?
let me know if you need more help