I have a 1988 Bonneville SE with AT, pdl, pw, ps, a/c with 185,000 miles. I have owned since it was new. Lately it has developed 2 problems. The first is that the battery discharges overnight. Sometimes just a fraction of a volt and sometimes enough for the car to not turn over. I pulled the fuses one by one and still couldn't tell what was causing the problem. I guess it could be any part of a wiring harness somewhere I don't know.
The second problem is I am experiencing an erratic idle and cruising rpm while driving. It usually starts about 5 minutes after I start driving. The idle goes up and down as I am sitting at a light and the rpms go up and down as I am cruising along, say at 35mph. The car accelerates fine if I step on the accelerator with some pressure. The ses light comes on periodically so I jumpered the connector and it showed a 44 code. I have a new oxygen sensor already so I thought I might just put it in and see what happens.
I just got done working on my daughters 1995 Grand Am which included cleaning the passage from the EGR valve. It was throwing the code for the 3rd solenoid on the EGR valve. Cleaning the little 1/4" passage on the EGR solved that and a code hasn't popped up since. Should I clean my EGR valve? I don't think it has been done since the car was new. I also have a couple wrecking yard spare egr valves also to try. Let me know what you think. Engine coolant sensor? IAC? Intake air temp sensor? MAF sensor? Thanks for any help. Gary

I would start with changing the O2 sensor and see what that does. Also cleaning the MAF and EGR wont hurt. You could also try doing a seafoam and see if that helps. I've seen that stuff do wonders on a car.