Simple enough:

My 2004 Hatchback has it's engine revving randomly up and down between idle and 2500 RPMs. it happens when it's at still, in park or in neutral.

It's only been happening recently, the mileage is 50700 ish and I have no idea what's causing it and I'm afraid of taking it to a dealer because they'll just charge me all sorts of stuff, but it might be my only option at this point, unless one of you guys has had the issue and got it fixed.

Kthx