P1457 is the EVAP canister system, including the popular vent-shut valve underneath the left-rear seat. Check out this thread, I put something towards the bottom.
P1457 won't make the car run bad at all. It just means the EVAP canister & the related system of hoses & valves isn't airtight.
Check this stuff in this order. As soon as you find something that doesn't behave like it should, fix or replace it. Then hope it was the only thing wrong with the system...
Some background for the electrical troubleshooting:
All the solenoid valves have constant +12v supply from the main relay. When the ECM wants to energize a valve, it closes the ground side of it's circuit. If the +12v supply is broken, then the ECM can't energize the valve. If the wire to the ECM is shorted to ground, then the valve is energized even when the ECM doesn't want it to be.
EVAP Purge Control valve - between intake manifold & valve cover.
Valve should be normally closed, so it will hold vacuum when it's not energized. Ground is supplied by pin A6 of the ECM to open the valve. So jumper pin A6 to ground, turn on the ignition, and check again - this time it should NOT hold vacuum.
EVAP 2-way valve - underneath the car roughly under the left-rear seat.
It's a little can with 3 hose barbs & a solenoid valve attached to it. Leave the connection on top, disconnect both on the side, attach MityVac to lower one. Normally open, when the solenoid valve is energized, it should hold vacuum.
EVAP Vent Shut valve - attached to the charcoal canister underneath the car.
Normaly open - when ECM closes pin A4 to ground, it should hold vacuum.
EVAP Charcoal Canister - the big can under the car, about under the left-rear seat.
Leak test: Connect all the hoses together, plug the Vent Shut valve, connect the MityVac. Pump vacuum while watching the fuel
tank pressure (FTP) sensor. You can read FTP sensor voltage with a scan tool, or use a voltmeter between pins A29 & C18 at the ECM. Pump down to 1.5v & it should hold that vacuum for at least 20 seconds.
EVAP 2-way valve vacuum & pressure test.
If you get this far you'll want the manual for a good picture of how to connect the hoses. Keep pumping the vacuum pump & it should stabilize between 6 & 16 mm Hg of vacuum. Then pump pressure, it should stabilize at 8 mm Hg or more of pressure.
Then there's a test of the ORVR Vent Shut valve, which is located on top of the gas tank. You check vacuum & pressure at a couple hoses alongside the fuel filler pipe. If the valve is bad you drop the gas tank to replace it...