[B10alia]

If you're looking at the moisture issues section for the MAP sensors on the troubleshooting page, that information is out of date. By '94, the location of the sensor had changed, and they were no longer susceptible to the moisture accumulation issue. You could be looking at a failed sensor, or a cracked vac line. There's a hard plastic section in the MAP line that can crack, and rubber deteriorates over time.

 

[B10alia]

To the OP:
Have you solved your problem?

 

[B10alia]

Code 21 is for an oxygen sensor. If it has never been changed, it may well need to be. The MAP sensor being out of range could potentially cause the MAP to seem to the computer to be faulty. There's always a bit of confusion about oxygen sensors and these codes; I defer to Bob Lincoln, since he wrote the article I'm basing this off of.