Cadillac Repair: 88 caddy brougham, cadillac brougham, brougham

Question
i have an 88 cadillac brougham and the check engine light is on. how to i do a self diagnostic. the car starts and idles very poorly and is running very rich and drinks gas. How do i fix this?

Answer
1. Ignition ON. Engine OFF.

2. Simultaneously push and hold the OFF and WARMER buttons for 3 seconds and release them.

3.Diagnostic LETTERS/CODES will appear and eventually stop.

4. Write down EVERY LETTER AND NUMBER EXACTLY as it displays in the EXACT order in which it displays.

5. Turn ignition OFF.