My 2004 Civic check engine light illuminated - OBD code is P1457
The car was taken to my mechanics and they replaced the EVAP bypass vlave and fuel tank cap.

The check engine light came back on at about 1/2 tank - other symptoms are: Car is difficult to start and will not idle after fuel tank cap is removed, car re-fueled, and cap replaced. The Car will start and operate normally after being driven a block or two.

Does anybody have any idea what is wrong?

 

Several other components of the EVAP system can throw this code, for example a faulty Canister Purge Valve, Canister Vent Shut Valve, Vapor line, Circuit, or Canister.

Return your car to your mechanic to have these other EVAP components tested.