I am driving a 1995 Bonneville and, lately, whenever I am idle, at a stoplight for example, my oil pressure drops and my check engine light comes on. Any ideas on why this could be happening?
Sounds like your oil pressure is dropping at low RPM, which could be one of the following: low oil level, a bad oil pump, low viscosity oil, or worn bearings.
First step after checking the oil level is to check the oil pressure with a manual gauge.
May even be a failing oil pressure switch...