My 1988 Daihatsu Feroza is having some issues changing gears. when i take my foot off the accelerator and press the clutch in, it revs up about a grands worth, instead of the revs going down. this happened a while ago, and i replaced the oxygen sensor and it hadnt done it since, until tonight, and it did it worse then ever. i took to dropping the clutch/changing gears VERY quickly in order to try and keep the revs down so that it wouldnt take off on me or anything. would be great to know what the problem is and why its donig this, as well as how it can be fixed as i really need my car for work etc. thanks! Lia.

The issue is one of over-fast idling. First thing is to check coolant level in the engine. Make sure that the coolant is at the 'max' in the reservoir (1:1 mix of water : antifreeze). Low coolant would preve nt the ECU from detecting the car is at operational temperature. When the car is cold the ECU extends injection times to keep the car running but when warmed up the injection times are again shortened to reduce engine speed at idle. Also at idle, the Idle air control valve (IAC) on the throttle opens to allow air to by-pass the closed throttle plate. Check that as the engine gets warm that the coolant hoses to the throttle body become warm (showing that no blockage is preventing coolant circulation). Check that IAC air passage is clear and that valve can open freely. If the IAC coolant hoses are blocked or the valve is jammed open this would account for the very high idle speed. If everything looks OK check the PCV hose from the valve cover to the throttle and make sure that there are no blockages in it.