Help on a Subaru Outback with "galloping idle"?

I've got a 2002 Subaru Outback with what can best be described as a "galloping idle". The car runs fine (except for an occasional hesitation at acceleration), but when the car is idling, I can feel like the engine is revving up and down. When it starts, it's quite regular. Sometimes it's subtle, sometimes it quite pronounced. Sometimes, it doesn't do it at all. Naturally, that's usually the case when my mechanic is driving it.

I've had it in the shop twice and both times the mechanic has found nothing. I've replaced the fuel filter, the spark plugs, checked the air filter and flow, changed brands of gas, switched to higher octane levels and added fuel system cleaners. None of which have helped.

Has anyone encountered something similar to this? Have you figured out what may cause it?

Update:

1st, thanks!

2nd: the cycle is about once a second.

3rd: Happens w/ engine hot or cold, A/C or no (more pronounced with A/C)

4th: Mech. reports no faults on computer or sensors. I can have him look @ the speed sensor

May have them check&reset the computer.

9 Answers

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  • ?
    Lv 7
    1 decade ago
    Favorite Answer

    How much of a gallop is there?

    Let the car only warm up for 10-30seconds Do you drive long or short trips? What type of oil do you use? Every 24,000 km or 15,000 miles the ECM needs to be re-programed, when was your last annual service?

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  • Kim
    Lv 4
    4 years ago

    This is normal for subarus. I have heard my uncle say once you hit so many miles the check engine light will come on. My dads old Hyundai would have this as well as my boyfriends Subaru. Take it to a dealer to double check but I'm pretty sure it's normal..

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  • 1 decade ago

    This problem has got to be electrical in nature.

    Have your mechanic check and clean all of the sensors associated with the intake side of the engine (air temp, air volume meters, etc.). I'm thinking that one of your sensors are dirty (from oil blow by) and is giving bad info to the ECU.

    The next thing to check would be the ECU and so on.

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  • 1 decade ago

    Air conditioner compressor may be kicking in and out or the engine may be trying to keep a certain temperature by turning on the cooling fans and increasing idle speed.

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  • 1 decade ago

    If you allow the vehicle to idle before driving and only take it out on short trips ths will happen especially when you use the extras (radio, heated seats, wipers, and so on) Stop idling before driving and this will fix it over time.

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  • 1 decade ago

    well my bro sold a acura TL(1999) and it did that, he said: "something in the throttle or throttle body is causing that", try going to a tuner shop and ask them to take a look at the throttle and the throttle body.

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  • 1 decade ago

    Ask the mechanic to check your "speed sensor".

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  • 1 decade ago
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  • 1 decade ago

    www.ultimatesubaru.org

    look under new models and post question there...

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