Sounds familiar. I bet there are a lot more cars out there with this problem, some dont notice it and some learn to live with for a lack of exact inexpensive cure.
I was also told by my mechanic about the oxygen sensor. Also another culprit would be the mixture control unit. Also older cars with the mileage are not perfect in terms of sensors, compression, vaccum etc and the electronics tries to compensate for it.
As many expensive items are involved I just have learnt to live with it. But for some people who like their cars to be perfect it still bothers me. One thing I did do was clean the air flow valve with a throtle body cleaner and it did help but not completely. Also my oservation is the brand of gas does make some difference.
Sure would like some of the experts on the forum to comment on the problem.
If you do chase down the problem make sure to post the results.