Check Engine Light comes every few days

Is this an O2 sensor code? If so then check the wiring to the sensor. Since the light comes on every few days then it is intermittent. Once the fault goes away then the light goes out. Fault comes back and the light comes on. Check the wiring carefuly to insure there is not a bare spot somewhere and is touching the engine or some other metal part of the car. Check the connector to ensure it latches firmly. Check the terminals inside both of the connectors to make sure thye have not spread open, are not dirty, or corroded. I once found a connection inside a fuse panel on a 97 LHS car that was not stripped back far enough at the factory. This caused and intermittent open circuit to the fuel pump. I have also reapired many a lose and dirty connector causing the check engine light to come on. Also some aftermarket parts like O2 sensors, MAP sensors, etc are made cheap and fail soon after installation. You get what you pay for. Cheap is not always a bargain.