Engine lights suck.. help please.

won't help you with pre-obd, but the auto-zone diagnostics suck. they only want to sell parts and they don't know what they're doing. there are some problems that will make your car run like shit and won't set a code at all, and other codes are actually caused by something that the code won't tell you. for example, a bad fuel pressure regulator won't set a code, but can cause the engine to run way rich or lean. if the 02 sensor outputs the high or low voltage from the bad mixture long enough, FRED (F-in Ridiculous Electronic Device, aka ECU) will assume the sensor is bad and set an O2 sensor code. auto-zone won't tell you that.