Thanks to all that responded to my previous post.  I did a poor job of
describing things and sent confusing info.  Here is a better description:
When cold, starts and runs fine.  After two or three minutes of running
(heating up) I have rough idle.  When stepping on the gas to move the engine
stumbles and slowly gains speed.  It feels like a miss.  After about 2000
rpm it seems to smooth out and runs fine.  Runs fine at highway speed.  If I
disconnect the O2 sensor, problem goes away except for slightly rough idle,
but has plenty of power to pull from a stop, etc.  But (as expected) you can
smell gas in the exhaust, running rich with the O2 sensor disconnected.
Work done about 120 miles before the problem started:  Rebuilt injectors
installed and idle tweaked up a little.  Work done by a very competent and
experienced mechanic.
Any suggestions?

--
Loren Busch
"I ordered a feast in the hope that you would come."
"I came in the hope there would be a feast."
(From "Monument" by Lloyd Biggle Jr.)