I couldn't solve this problem.

My mechanic did smoke test;
Changed both oxygen sensors and mass air flow sensor with the original parts but still the same.
Then he asked me to buy gas cap but still the same..

Engine light goes away every 2-3 days when I run the car and come back after 2 days. I don't know what else I can do...

 

trouble lights are not shopping lists.
Try the troubleshooting here:
https://www.obd-codes.com/p0172

Or find a mechanic who knows how to do diagnostics and not change parts.