I went away for a month and my car was sitting in the driveway during that time. When I got back and started up my car, it started revving up and down. Why is this happening??? What can I do to fix it???

 

sounds like it's an idle air control valve issue to me. if you do a search on that topic and also search about revving or something like that you should be able to confirm (or disprove) that with the other posts people have made.

welcome to the board by the way! the search button is going to be your best friend, just like it is to the rest of us!

Bob

 

My first thought was also the IACV.

Another idea is that your battery might be in a partially discharged state from sitting for a month. So that could go away as you drive the car and the alternator charges it.

Bob

 

I had the same problem about a year and a half ago when I left my car at school during christmas break. I took it up on the highway and opened it up, and everything went away. I did get a CEL for the IACV, it just got a little stuck from sitting too long with out being turned on. Just reset the ECU after the problem goes away and so will the CEL

 

Carbond up IAC valve, take it off, a little carb cleaner in the passages, put it back on and drive her to clear it out. If that doesn't fix her then it may be going out.