P0441 OBD2 Code on 1996 Toyota Camry: Causes and Fixes

I own a 1996 Toyota Camry, and the check engine light frequently comes on with fault code P044-1. I've already replaced the evaporative emission control system modulator valve and some hoses, but the issue persists—appearing roughly once every month. After clearing the code, the car runs normally for about a month before the problem returns. When the code activates, the engine idles roughly. Any advice on how to resolve this recurring P0441 issue would be greatly appreciated.