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kserre2000 4/17/2013
1997 Cadillac DeVille Base 8 Cyl 4.6L - Engine
when slowing down or idling the engine vibrates the car. already replaced spark plugs and wires. also had fuel injector cleaned. only has 120,023 miles. just started yesterday . mpg went from 25 to 18. check engine light is on, but codes were for new spark plugs and wires. we cleared the reader and it still says the same thing.
1 Answer
  • Jimm
    Jimm 4/21/2013
    First step - have the check engine light or stored fault codes scanned - for free - at any local auto parts store; Advance Auto, Auto Zone, NAPA. Then, post a reply as 'add answer' with the specific fault code for more assistance.

    Possible Causes of Engine Hesitation or Stumble:

    Dirty fuel injectors (cleaning the injectors often fixes this)
    Dirty air filter (change filter)
    Dirty / clogged fuel filter (change filter)
    Bad MAP (manifold absolute pressure) sensor
    Bad TPS (throttle position) sensor
    Bad or dirty MAF (mass airflow) sensor
    Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
    Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
    Bad gasoline (fuel contaminated with water or too much alcohol)

    Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

    Dirty or worn spark plugs
    Bad plug wires
    Weak ignition coil
    Wet plug wires

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