My check engine light has been on for about a month. I had it checked and was told it was my o2 sensor, I had it replaced and the light stayed on. I had it checked again and was told my o2 sensor was registering a vacuum leak, however it could not be located. On cold starts I get hesitation and rough idle, but when it warms up these problems cease. Any suggestions?

TRYING TO AVOID DEALER COST

Try the EGR Valve. When it goes it sometimes gives codes for the 02 sensor.