Manifold Absolute Pressure sensor, very common to go bad on Escorts. If yours is a MAF engine, it may not have one, though. You can tell if it is MAF by looking for an aluminum (typically, though some are black ABS plastic) housing with a large electrical connector somewhere in the airflow path between the air cleaner and throttle body. Don't confuse this for an Air Charge Temperature sensor. That is small and usually only has 1 or 2 wires going to it. The MAF sensor will have 4 - 5 wires.
If it is the MAP sensor, it is typically mounted on the firewall, and will have a vacuum line and electrical connector. Usually a small black box, a bit smaller than a pack of cigarettes.
Best way to diagnose this is to go to your local parts store and pick up a code scanner. An 89 Escort will still be OBD I, so the scanner for that will be cheap, about $34. It comes with a manual that tells you how to use it and descriptions of what the trouble codes mean.
