Of Mitsubishi variant, the ISC (Idle Speed Control) servo valve need to be cleaned especially the secondary gear support shaft. This support shaft is basically a hollow sleeve that accepts the secondary gear which will turn according to the engine load demand by opening the bypass air passage from below the throttle body to allow more air into the throttle body which will raise the rpm especially during idling where the vacuum is greatest. These transfer gear may crack as they are made of plastic and if true will need to be replaced.
The components making up the ISC servo valve unit basically comprise of gears very much like what you see inside a clock where the gears are inter-connected. To the left you can see from top right to bottom and left respectively are the secondary support shaft which is hollow, the spring for the secondary gear, the secondary gear , the white driven gear which has a flat damper washer attached to it. This white driven gear do wear out over time and will display some slight protrusion at the centre as illustrated below. If the leg below this gear is held tight while the head part is turned, excessive free play maybe noted and this part must then be replaced.
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