[dj1111]

I had similar symptoms earlier this year on my 2000 SL2. And my 98 Venture van suddenly wouldn't start about a month ago. If it did start it wouldn't hold an idle. But when you say 1 and 5 rpms do you mean 1000 and 5000? Mine would never run that high. Turns out both of them were having problems with the idle air valve in the throttle body. This is the thing that allows air to get in the engine when the throttle plate is closed (at idle). It has to move precisely with no restrictions (deposits and gunk) in order for the engine to idle. In both cases all it took was removing and thoroughly cleaning the throttle body, and the afore mentioned valve. My Saturn was particularly easy to take apart and reassemble. Having a manual to help you with the process helps.