UK Car Repair: reving higher?, vacuum lines, rule of thumb

Question
hi ya. please could u tell me why my engine keeps reving higher and higher by its self. if u blip the gas it wil come down then start rising randomly.i have tigra

Answer
Hi Julie, when you open the throttle, it allows air to draw in and it is this air that causes the revving. If you have a high rev then you have a leak of air either a vacuum or inlet manifold gasket. Start the car and listen for a hiss (this is where the air will be rushing in ) look for open ends of vacuum lines. Alternatively, it could be a faulty idle speed control valve, but look at this second as i follow the rule of thumb, cheapest first and work up. let me know what happens[ _ Paul