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1992 Mercedes-Benz 300E Question: rough idle



chuckp, Park Ridge, IL, September 25, 2009, 12:05

My '92 300e with 134k miles has a persistent rough idle. changed fuel filter, but it didn't help. What could be wrong?

2 Answers
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  • Medium-star Best Answer
    patrick mannion from Greg Solow's Engine Room, September 25, 2009, 12:18

    Was it only the coolant flush that made the engine idle rough? If so changing the fuel filter shouldn't affect anything. Could water have got on ignition components or a vacuum hose or electrical connection have been knocked off. If it idled smooth previously nothing should have changed. Some cars get air locked and pockets of air in the cooling system will dissipate after a while running the engine with the heater control on full hot, and allowing the engine to idle frequently topping up the coolant level as required.
    After that there would be too many possibilities to guess at or express an opinion on what may be the problem without being able to carry out some tests first hand.

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    Visitor, September 10, 2010, 12:03

    A mechanic with considerable knowledge and experience of Mercedes tells me the problem could be the oxygen sensor, which is the original part. What's your experience
    with the oxygen sensor? My car does not have a Check Engine light.

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  • Answer #2

    Visitor, September 10, 2010, 05:01

    You need to check for error codes first. Clear each one individually, one by one, then drive as normal and the true errors will register again, thus triggering, or not triggering the check engine light.
    The error code will you to the right area to troubleshoot the problem correctly.

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