Old post, but in case there is another question about this issue for a 1st Gen Expedition-
Perform a Diagnostic Scan:
-Use an OBD-II scanner capable of reading suspension system codes to identify specific faults.
Inspect Air Suspension Components:
-Check for leaks, damaged air springs, or debris around the suspension.
Check the Compressor and Switch:
-Listen for the compressor's sound when the system adjusts; ensure it’s working.
Reset the System:
-Some issues are temporary and can be reset by disconnecting the battery for a few minutes, but persistent problems need repair.
Obviously if none of this works, then going to dealership or mechanic to get it figured out.