car revving without me touching accelerator?

i have an 02 clio that ive had a few months and just recently it has started whilst im driving the engine management light will come on and the car wil rev by itself without me touching the accelerator, so the car drives but only by me using the clutch and the break, its crazy as i can turn off for 5 mins and restart and it will be fine, just want to know if its a big job as if its small i will get fixed, if not its not a huge deal to me! thanks