Probably a small vacuum leak. I found one in mine some time ago. There's a vacuum reservoir under the right side of the intake manifold. In front of it (towards the p/s pump) is a vacuum hose with a small check valve. My check valve had cracked from years of heat and was just enough of a leak to put a small 'bump' in the idle. See: 'Vc tank' at http://www.subaru-svx.net/photos/files/Beav/5309.gif
Others have found loose intake plenums and manifolds, etc. Vacuum leaks are the most common cause of idle roughness (with no other symptoms.)
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Last edited by Beav; 11-29-2002 at 04:02 PM.
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