either idle control valve as above or throttle position sensor, more then likey the icv though, two bolts 8mm iirc, if you do go for a replacement make sure you match it up by comparing the underside (side which bolts onto the engine ) and matching one with the same pattern up, there are two types one with circle cut outs and one with a more square cut out


shouldnt be no more then 25 quid for a scrappie