I have the 97 FSMs. DTC P0442 is the closest I can find - "EVAP Control System Small Leak Detected".
Cracked or Punctured EVAP canister
Damaged source vacuum line, EVAP purge line, Evap vent hose or fuel tank vapor line
Poor connection at PCM
Damaged harness to EVAP canister vent valve, EVAP purge valve, and lastly, fuel tank pressure sensor
So, after checking that the gas cap is secure, you have several choices.
Try another gas cap to ensure your cap is not defective...
Trace all rubber and hard plastic vacuum hoses/lines looking for cracks, disconnected/broken connectors/poor conections (look closely for cracks in the vacuum lines. Even hairline cracks can cause leakage). Replace any cracked sections/lines...
Inspect connectors at PCM and on PCM wiring harness for damaged terminals/connections
Make sure electrical connections are good on EVAP canister, the EVAP purge valve and the fuel tank pressure sensor.
My bet is a cracked or disconnected vauum hose/line.