Why is my 1994 E-Class revving every 15 second?

My 1994 Mercedes-Benz E-Class Coupe 2.0 is revving every 15 second without any input from my right foot. What's the issue?

Is it worthwhile to repair my old car?

I have a three-door 1997 Toyota RAV4, which I've owned since 1999. The subframe needs welding, plus a few other bits. It will cost around £800. Would you consider it worthwhile? I do about 3000 miles a...