As you may expect since various specialists couldn't solve the problem, not sure how much can be done over the net. I'll try to summarize the problem and put it in a perspective for further help.
1st what year is this car, how many miles etc.?
2nd any codes (check engine) were given to you from the specialists?
3rd did they check for leaky injectors?
4th Black smoke etc
This is what we have:
A. Rough idling
B. Too much gas consumption
C. Blown- left and right- O2 sensors.
One of these specialists has to say something about ABC above!!!
when engine run too rich/too lean rough idling is the norm. Too much gas is rich, O2 sensors go nuts over their limits trying to correct/trim mixture and then fail? Cat will not survive (since 1999) all this mess!
Anyone wishes to take it from here?