1985 Fiero GT 2.8L

First noticed problem/change: I have to crank the engine 3 times
before it will start. It was starting on the first cranking of the
engine.

Second problem/change:  I locally drive to somewhere, park and turn
off the car, short time afterwards, engine still hot, I try to start
and it acts gas starved, putt-putt-putt, give more gas,
putt-putt-putt, sometimes would fire up and run, sometimes not.

I can start and run the car short distance and not notice any problem
other than the starting on 3rd time cranking the engine.

ECM Error Codes: 13 oxygen sensor and 44 lean mix.

I am going to replace the oxygen sensor with a new one tonight.

I hear the fuel pump come on for 2 secs after ign key turned to on.  

What else could be causing the lean mix condition?