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What causes a car engine to idle rough and miss?

This car is a V8, always serviced



Plugs and wires changed, O2 sensor changed, distributor new, premium gas used, injector cleaner used -- still rough idle and miss Thanks!



Any ideas? 1990 Cadillac 4.5 liter 99K
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Comments

  • edited October 2009
    I'm assuming a new cap and rotor were part of the distributor replacement.

    Has a compression check been performed? Perhaps one of the valves is burned or not sealing properly.
  • edited October 2009
    When was the last time the fuel filter was replaced.
  • edited October 2009
    Compression test.
    Check for leaky EGR valve.
  • edited October 2009
    Look for vacuum leak
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