HELP 93 Camry power surging? Low idle

Hey all. Ok im going to do my best in describing my problem in hopes that someone out there can help me in fixing my car issue. I have a 93 v6 camry. Ok so every once in a while my car will power surge and sometimes hesitate. It doesnt happen all the time maybe like once a week but anyways it only does it when you first start to accelerate. Today my husband was messing around with it and just tapping on the gas pedal and letting up really quick and it would power surge and act up. Also every once in a while it will idle low at about 500- 600. Now other than that the car runs great. We do need a new o2 sensor so im not sure if that could be causing the power surging or not. We live on a very limited income and this is our only car so im desprate to get the problem fixed before it gets to big. Also is it a possibility that the timing belt or accessory drive belt could be doing this? The only reason I ask about those two parts is we recently took it in for an oil change and they told us we needed to get those replaced. Anyways help me !

thanks

-sara