Check engine light came on tonight after having the car for 4-5 days, problem?

What is your question?

Car is not running rough idling or accelerating. Hearing a slight tap noise when idling but doesn't sound like it's in the motor. Car doesn't stall at any speed.

What makes this problem better or worse?

Light popped on randomly on a short drive home

How long has your 1999 Saab 9-3 had this problem?

One night