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Thread: Fluctuating MPG Gauge

  1. #1
    Join Date
    Nov 2005
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    Mo!
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    Default Fluctuating MPG Gauge

    I drove the wife's car (a '93 525i automatic w/~140k) tonight after she reported it seems sluggish and low on power.

    She's also reported some hesitation upon first throttle input from a dead stop. I could probably be convinced that there's a bit of hesitation and perhaps the response/power is down a bit.

    I did notice the MPG gauge fluctuated when going uphill at constant speed with constant light/moderate throttle input. The gauge almost looked like I was modulating the throttle. Just wondering, after reading some posts here, would that make any of the experts suspect an O2 sensor - to our knowledge this hasn't been replace yet.

    She's also noted an occasional wandering temperature gauge, so I'm going to check the sensor connections and also operation with my DVM. Just curious, could a problem with reading proper coolant temperature cause any of the secondary issues (low power, hesitation, sluggishness, etc.)?

    Within the last 20k miles, we've done a cooling system overhaul (fluid, hoses, water pump, tstat, etc.), new belts, sparkplugs (NGK), fuel filter, and air filter.

  2. #2
    Join Date
    Dec 2003
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    Eastern Tennessee USi
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    14,821

    Default

    you could either have a faulty thermostat which can cause all of the symptoms or a bad O2 sensor. bouth can cause erratic sensor readings as they are all a part of the big picture.

    Quote Originally Posted by shadowpuck
    I drove the wife's car (a '93 525i automatic w/~140k) tonight after she reported it seems sluggish and low on power.

    She's also reported some hesitation upon first throttle input from a dead stop. I could probably be convinced that there's a bit of hesitation and perhaps the response/power is down a bit.

    I did notice the MPG gauge fluctuated when going uphill at constant speed with constant light/moderate throttle input. The gauge almost looked like I was modulating the throttle. Just wondering, after reading some posts here, would that make any of the experts suspect an O2 sensor - to our knowledge this hasn't been replace yet.

    She's also noted an occasional wandering temperature gauge, so I'm going to check the sensor connections and also operation with my DVM. Just curious, could a problem with reading proper coolant temperature cause any of the secondary issues (low power, hesitation, sluggishness, etc.)?

    Within the last 20k miles, we've done a cooling system overhaul (fluid, hoses, water pump, tstat, etc.), new belts, sparkplugs (NGK), fuel filter, and air filter.
    95 E34 530I V2.37
    ===========
    Those who make peaceful revolution impossible will make violent revolution inevitable.

    John F. Kennedy

  3. #3
    Join Date
    Nov 2005
    Location
    Mo!
    Posts
    90

    Default

    the tstat was part of the cooling system overhaul recently, but its always possible I received a DOA part. The temp gauge wanders on very rare moments - and always comes back to the "proper" temperature.

    Gas mileage appears to be down just slightly, I'm going to suspect O2 sensor at this point, but I'll check all the other components first...

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