1995 Bonneville SSEi Supercharged, Irratic idle
 

The car warm or cold will not idle at one speed. When i first start it cold it will idle up to around 1800rpm's or so and then when it should drop to normal idle speed of about 1000rpm's it keeps going down and almost stalls and then it will idle up again and down again and never stays at the same rpm's. Once it is warm I can stop for a light and the idle will drop to about 800rpm's or so and almost stall. When I stop for a light the idle does not race it just drops. It may not race because I have it in drive.
I have recently replaced MAF, Ignition control module, plugs, wires, 02 sensor, coil packs, IAC valve and about two years ago the EGR valve.
I was having vacuum leak issues with the EGR tube, but I believe they are taken care of.
When the idle drops you can smell it chocking out, runs rich.

When I had these problems it was my egr valve. I know you said you replaced it, but might be worth checking for a clog or other similar issue. Check for vacuum leaks also. Spray some TB cleaner around your lines and see if it affects your idle.

Have you checked fuel filter / fuel pressure? I don't think this would be the cause, but never hurts to check

Check for vaccum leaks.Pull your IAC and clean it..and maybe even test your MAf senso