Engine cutting out, high revs when idle and car moving under own power

brought my first car 6 months ago and it started off fine although 12 years old it has only now done 42,000 miles over the last couple of months it has started cutting out every now and again with the engine light comming on then kicking back into life (the engine was running the whole time).

2 weeks ago the engine light came on and i lost all power on the accelerator pedal going 30, changed down to 2nd and it jolted around and then worked again.

today i was driving along and the revs when changing gear were all over the place and i drove along a back road in 3rd with the car under power yet with no feet on the pedals, sat at a junction in 1st with my foot on the clutch the rev counter was on 3,000 rpm when its normally around 1,000.

since i have owned the car i have done nothing to it or added anything not so much as a new bulb. any help you could give would be greatly appreciated as i know barely anything about cars and to be able to go to the garage with atleast some idea would be great, many thanks


Tom