Ive been trying to diagnose a rough idle / chugging. Only runs rough after warmed up and idling. Driving at any speed the car runs perfect.

Just replaced the O2 sensor, took the car for a ride and still chuggs. I let the car sit on the driveway idling and could hear a distint "whining" noise coming from the back/rear of the car associated with a slight hissing type noise. The noise is intermittant, it will whine(and hiss) for between 10 seconds to a minute or so...then stop for a few minutes, then resume etc etc.

I would think the fuel pump? However the pump is only about 2 years old and was installed by a reputable shop. The car is pretty low on gas too... I was thinking of filling the tank and if the whining goes away that means the pump but I dont know..

Any suggestions? I'm going crazy here

 

sounds like the fuel pump,or gas cap. let it run for about ten mins.again and untwist the cap slowly ,see if it makes the hissing sound ,my moneys on the pump,later jimmy