Engine Performance problem
1999 BMW 318 4 cyl Two Wheel Drive Manual 108708 miles
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WE REPLACED THE MUFLER AND CATALYST BECAUSE WE WERE GETTING A BAD CATALYST CODE ON THE COMPUTER NOW WE SOLVED THAT
BUT WE ARE GETTING A PO455 WICH IS THE EMMISSION CONTROL APARENTLY HAS A LEAK ...
WHAT SHOULD I DO

You may have left the fuel cap loose during a recent trip to the gas station, clear the fault and be sure the cap is tight. The fault code is for a gross leak detection and usually means you left the cap off or loose.