I've noticed and excess of CEL threads where they haven't had the codes read.
Can we have a sticky stating to get the OBD code read and check OBD-II Check Engine Light Trouble Codes
That site has symptoms and diagnosis of almost every code I've seen people question. This could possibly decrease the amount of these threads greatly. Also, without knowing any codes their car has, it makes it hard for the rest of us to diagnose issues they have with how their car is running.