Recently had my car serviced and prior to this service my idle speed when warm was about 900rpm. Now when warm it sits above the 1000rpm mark... there appears to be no throttle stop idle adjustment - can anyone tell me a) the reason for the faster idle and b) how to adjust it? The car is a '97 tdxs, with everything else fine. The mechanic did say the air filter was very dead, so this could be dragging it down - but as I understood it, the idle speed should be around 850? Thanks! P.