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Jumpy idle, harder cold starting than usual 850 1994

posted by  jean-philippe gauthier on  Thu Nov 30 18:51 CST 2006
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last visit: Thu Oct 1 14:55 CST 2009
[RELATED]

I would suggest you to check the constant idle valve, near the intake manifold. It is a cylindrical device with 2 pipes connected to it. Because this valve regulates the air intake to keep stable engine idle speed, it can create a rough idle if it doesnt work properly. Remove the trottle body plastic cover and you will see it easily. Sometimes it sticks close when dirty. You can feel the valve in it rotating if you rotate the entire unit in your hands.

Clean with some carb cleaner if it sticks.

Also: check the plastic tree shaped pipe connector near the valve. The rubber elbows connecting the vacuum lines to it are prone to failure (check for small cracks in the rubber).

Vacuum leaks are always difficult to trace because there are lots and lots of vacuum tubes under the hood: PCV, EGR, boost gauge, brake booster, EVAP... Good luck!

JP






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