97 jetta idle problems

hey there everyone, So i have a 1997 VW jetta TREK 2.0l 4cyl, manual tranny, all stock. I've had an idle problem for quite a while. The idle will bounce between 900 and 600. When the AC is on, it is much worse and my car will sometimes die when it is brought to an idle. Doesn't always start right away anymore. It seems whenever something turns on i.e. (fan, ac) the idle is affected. I was thinking throttle body? battery? any tips? just wondering, hoping i could narrow it down with some input before i take it on myself. Thanks for any help.

Test the voltage with the car off. Then with the car on, and then bring the idle to 2K, and then turn all the accessories on and test the voltage again. That you could start with. Then you could test the alternator, its voltage and the ohms.

Check all the threads on throttle body cleaning.