97 runs rough at start

97 w/177k occasional (every few days) running/idling rough just when I start it first thing in the morning and runs like it is almost missing for a few miles and then clears up. Still throws a CEL but disappears before I get it to the mechanic to read it. Had the first in the line O2 sensor replaced a few months ago. New plugs and wires about 70k mi ago. Since it is hard to time this to get it read at the mechanic, any suggestions on what it could be at this point. Trying to take it on a trip this weekend.