1995 Pontiac Trans Sport Malfunction Codes 33 and 34

1995 Pontiac Trans Sport, 121,000 miles, 3.1, vehicle acceleration goes up and down and stalls when engine is cold. Spark plugs, distributor cap, rotor, MAP sensor, throttle position sensor (TPS), and idle air control valve, have all been replaced. Timing on vehicle was adjusted and this took care of the problem for about two weeks. I did not disconnect the battery to clear the MAP sensor code (if that is how to clear the code). Could this be the problem ? or something else?

Any help would be most appreciated.

Thanks!