Re; 2000 Catera, 60,000mi.
Is anyone familiar with the factory idle/normal RPM settings? The last few days the idle has had me glancing at the RPMs as the engine gets way down to about 400 (almost close to stall) then shoots up to about 8-900 while stopped in drive. Also fluctuates like this during cold-start till warmed up. Could old battery or alt. be suspect? This is not a serious situation now 'cause she runs perfect 98% of the time, but could it be a train commin' down the tracks?

Sounds like the cold start injector is having problems to me

My 99 idles at 500 rpms. When coming to a stop it drops to about 400 and then goes back to normal. I think the dropping problem is a vacuum leak. Check you vacuum lines and use some injector cleaner (Sea-Foam!) Car seems to idle better with it.

I suspect a vacuum leak too. I seen this problem on several cars before. I don't say it should be that, but it could be.

Ehm, does foam show anything on a vacuum leak?

hmmmm