5w30 would not be recommended for a 1FZ at all.
10w30 or 15w40 would be better depending on the climate where you are.
In really cold regions, you might need different grades summer and winter, but I'm sure this isn't likely the case in Cali
5w is to light, your asking for problems.
A lot of...
Your brother let the pixies out!
Never trust brothers with cars!
Until you check the oil level, why panic?
Could be an issue with you oil level sensor wiring. Go check your oil level, and check for loose/cracked/ damaged wiring harness, or dirty connection on the oil level sensor.
In the...