we found leak around pcv valve(?), changed it & grommet. light went out then cam

What is your question?

just purchased car & light came on next day. why would it come on and stay on steadily. then go off when pvc & grommet were changed only to come back on 2 days later? no performance problems!.

What makes this problem better or worse?

Nothing. Just aggravating and worrisome .

How long has your 1999 Toyota Avalon had this problem?

3 weeks