OK, now I am confused. I let this one go when I first read it, knowing that the only way a 90 300CE could turn a light for Air injection would be if it was a California car.
No having much experience with Ca. emissions I figured I had nothing to add. I read right over the MAS sensor without putting 2+2 together. The Mass Air Flow sensor doesn't start till 1993 on 124 cars. I don't know what they would have replaced on a 90 model unless it was the whole airflow sensor (plate).
Is this a Ca emissions car? If not is it really a 93 or newer as the KE cars shouldn't have a airpump code on federal cars or at least it shouldn't light the light?
Whatever the situation, you might want to get a second perfessional opinion as in my book three strikes and your out! The parts that were replaced (with the possible exception of the O2 sensor) don't seem to be related to your fault code.