Idle is PCM controlled by various sensor inputs. Saturn had a problem with coolant temp sensors that where cracking , leaking and /or had corroded terminals. Unplug your coolant temp sensor and check the terminals for corrosion , check for wetness inside and look at the plug for corrosion. If any wetness or corrosion is found, replace the coolant temp sensor.
The other area to check requires a scan tool to allow you to adjust idle manually through the IAC to determine if the IAC is working properly. Coolant temp sensor can be checked to see if it is reading properly with the scan tool.
Have you had a check engine light and if so, what were the codes? This will help further for either you to fix or if needed, have your tech fix.
Get back to me with the engine and model and we can get further into what to check. SL1/SL2.
In the end. If it's not vacuum which from your description, it isn't. It lies between the IAC or temp sensor. Temp sensor will create erritic idle.
The more information you can give me, the quicker we can get an answer.Meawhile, try checking that temp senor as described. It is on the trans side of the engine.