B757 FLT CREW HAS SMOKE AND FUMES AFTER TKOF AND RETURNS TO THE DEP ARPT.

Narrative

ON ARR AT COCKPIT; I STOWED MY BAGS AND PROCEEDED OUTSIDE THE AIRPLANE FOR THE WALKAROUND. MEANWHILE THE CAPT PERFORMED THE NORMAL PREFLT DUTIES WHICH INCLUDED STARTING THE APU. THE ACFT HAD A DEFERRED APU WHICH WAS NOT NOTICED BY EITHER OF US IN THE PAPERWORK AT FLT OPERATIONS. WHEN I RETURNED TO THE ACFT; THE FLT ATTENDANTS WERE LEAVING AND COMPLAINING ABOUT MIST AND ODOR IN BACK OF THE PLANE. I WENT UP TO THE COCKPIT AND MAINT AND THE CAPT WERE TALKING ABOUT THE CAUSE OF THE SMOKE. THE MECHANIC SAID HE SAW SOME SMOKE IN THE E&E COMPARTMENT AND HAD CALLED THE FIRE TRUCKS TO RESPOND. WE LEFT THE AIRPLANE AT THAT TIME. THEY LATER RELEASED THE AIRPLANE AND THE MECHANICS PUT GND AIR ON AND RAN BOTH ENGINES AND PACKS AND THE SMOKE AND SMELL CLEARED. WE BOARDED; STARTED BOTH ENGS; TAXIED AND DEPARTED RWY 30 WITH NO FURTHER INCIDENTS. ON DEP WE NOTICED A LITTLE ODOR THAT SMELLED LIKE OIL. THE CAPT CALLED BACK TO THE FLT ATTENDANTS WHO REPORTED SOME SMOKE COMING THROUGH THE AIR CONDITIONING DUCTS ALONG WITH THE SAME ODOR WE WERE SMELLING. THE LAV SMOKE DETECTORS WENT OFF AND THE SMOKE CONDITION CONTINUED. AFTER FOLLOWING CHKLIST PROCS; WITH NO IMPROVEMENT TO THE SITUATION WE RETURNED TO THE DEPARTURE ARPT AND DEPLANED THE PAX AT THE GATE.