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Jumpy idle, harder cold starting than usual 850 1994

posted by  adumas on  Sun Nov 26 11:16 CST 2006
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Hi,
My 94 850 usually has a smooth idle and starts very quickly, hot or cold.

Now the car idles normally for a few seconds, drops maybe 200 rpm's and after a second or two of rough idling, jumps up 200-300 rpm's past normal idle. It stays at normal idle for an indefinite time, anywhere from a few seconds to a couple minutes, then repeats the lower/faster idle sequence.

The same time the above began to occur, starting the car began to take much longer, if it has been sitting for longer than 10-15 minutes. The engine starts, runs roughly for a few seconds, then acts normally, except for the idle problem. The car starts normally if it is started within 10 minutes of being shut off.

The plugs, cap, rotor, air filter and flame trap were changed 2-3 months ago during normal maintenance. The car has 150K on it, I've had it for the past 50K miles. None of the fuel system parts have been changed since I've owned it except for the fuel filter which was changed at around 110K.

The car's symptoms remind me of the 140's cold start injectors when they would start leaking and drip fuel into the intake which would cause the same jumpy idle.

Any ideas on what could be causing the problem?

Andrew Dumas








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    Jumpy idle, harder cold starting than usual 850 1994

    posted by  someone claiming to be ksg on  Tue Nov 28 02:30 CST 2006 [RELATED]

    Should we assume the check engine light is NOT on?

    Seems like either the engine controls don't know what the temperature is, or there's something wrong with fuel flow.

    How about warming up? Does the car lack power when not fully warm? If so I would suspect an air leak (as the other post said) and/or ECT temp sensor signal not right. That is, it could be anything which would not let the fuel mixture get rich enough when cold. Seems like fuel mixture problems would eventually set a code.

    Also if you start the car once and DON'T let it warm up, is it easy to restart then? What about performance at full throttle (with engine warm)? These things might suggest the fuel flow is not adequate (fuel pump, dirt in tank?). These issues might not usually set a code.








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    Jumpy idle, harder cold starting than usual 850 1994

    posted by  someone claiming to be fixit2003 on  Mon Nov 27 04:06 CST 2006 [RELATED]

    Maybe remove and clean the throttle body and associated flame trap tubing connections. Might be time to clean the oil seperator under the intake manifold. Check for cracked air intake accordian tube.








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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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